Introduction to Medical Terminology

Medical terminology is language that is used to describe anatomical structures, processes, conditions, medical procedures, and treatments. At first glance, medical terms may appear intimidating, but once you understand the standard structure of medical words and the definitions of some common word elements, the meaning of thousands of medical terms is easily unlocked.

Most medical terms adhere to a fixed structure of a prefix, a root, and a suffix. These word components are assembled like building blocks to create a vast vocabulary.

The physicians of Greece are considered the founders of rational medicine, and medical terms are primarily derived from Greek and Latin.1 Over the centuries, the language of medicine has evolved into multiple national medical languages. Today, medical English is the primary language for international communication. It is used in most influential medical journals and has become the language of choice at international conferences.2

Basic Term Structure

Medical terms are composed of the following standard word parts:

  • Prefix: When included, the prefix appears at the beginning of a medical term and usually indicates a location, direction, type, quality, or quantity.
  • Root: The root gives a term its essential meaning. Nearly all medical terms contain at least one root. When a prefix is absent, the term begins with a root.
  • Suffix: The suffix appears at the end of a term and may indicate a specialty, test, procedure, function, disorder, or status. Otherwise, the suffix may simply define whether the word is a noun, verb, or adjective.
  • Combining vowel: A combining vowel (usually the letter “o”) may be added between word parts to aid in pronunciation.

Breaking a word down into its component parts should help readers ascertain the meaning of an unfamiliar term. For example, hypothermia has the prefix hypo- (meaning below normal), the root therm (heat or warmth), and the suffix -ia (condition).

Prefix, root, and suffix for hypothermia.

Word Roots

A word root is the foundational element of any medical term. Roots often indicate a body part or system.

Common word roots:

brain encephal
ear oto, aur
eardrum tympan, myring
eye ophthalm, ocul
face faci
nose rhin
skull crani
tongue lingu
tooth odont, dent
Heart and Circulatory System
aorta aort
arteries arteri
blood hem, sangu
blood vessels angi
heart cardi
veins ven, phleb
Bones and Muscles
arm brachi
back dorsa
bone oste
foot pod, ped
muscle myo
rib cost
shoulder scapul
wrist carp
Digestive System
appendix append
colon col
esophagus esophag
intestine (usually small) enter
kidney ren, neph
liver hepat
stomach gastr
Other Common Roots
cancer carci
drug chem
electric electr
heat therm
knowledge gnos
life bi
pressure bar
returned sound echo

Compound Words

A medical word may include multiple roots. This frequently occurs when referencing more than one body part or system. For example, cardio-pulmo-nary means pertaining to the heart and lungs; gastro-entero-logy means the study of the stomach and intestines.

Combining Forms

A combining vowel is used when a root is followed by another word part that begins with a consonant. A combining vowel (usually the letter "o") is added after the root (e.g., neur-o-logy) to aid pronunciation. The root and vowel together (e.g., neur-o) are called the combining form. For simplicity, the word part tables do not include combining vowel options.

Root, combining vowel, and suffix for neurology.


A prefix modifies the meaning of the word root. It may indicate a location, type, quality, body category, or quantity. Prefixes are optional and do not appear in all medical terms.

Common prefixes:

large macro-, mega(lo)-
small micro-
half semi-
half (one side) hemi-
one mono-, uni-
two | three | four bi- | tri- | quad(ri)-
equal equi-
many poly-
above normal hyper-
below normal hypo-
normal/good eu-
Time or Speed
before pro-, pre-, ante-
after post-
back/backward retro-
again re-
fast tachy-
slow brady-
new neo-
time, long time chron-
Location or Relationship
away from ab-
above supra-
around peri-
across trans-
between inter-
out of, outside ex-, ec(t)-
self auto-
through, completely dia-
together con-
toward ad-
within, inside end(o)-
Function or Quality
against anti-, contra-
bad mal-
cause eti-
without a-, de-
abnormal, bad dys-


Medical terms always end with a suffix.3 The suffix usually indicates a specialty, test, procedure, function, condition/disorder, or status. For example, “-itis” means inflammation and “-ectomy” means removal.

Alternatively, the suffix may simply make the word a noun or adjective. For example, the endings -a, -e, -um, and -us are commonly used to create a singular noun (e.g., crani-um).

Although the suffix appears at the end of the term, it often comes first in the definition. For example, appendicitis means inflammation (-itis) of the appendix.4 Accordingly, it is sometimes helpful to read unfamiliar medical terms from right to left.

Occasionally, medical terms are composed of only a prefix and a suffix. For example, apnea includes the prefix a- (without) and suffix -pnea (breathing).

Common suffixes (letters in parentheses are not always present):

Basic Noun and Adjective Suffixes
(noun form) -a, -e, -um, -is
causing -genic
condition -ia, -ism, -sis, -y
specialty -iatry, -iatrics, -ics
specialist -ian, -ist
structure -um, -us
small, little -ula, -ulum, -ulus
study of -logy
pertaining to -ac, -ar(y), -(e/i)al, -ic(al), -ior, -ory, -ous, -tic
Tests and Procedures
removal of -ectomy
image/record -gram
recording instrument -graph
process of recording -graphy
cut in -otomy
visual examination -scopy
opening -stomy
Pathology or Function
blood (condition of) -emia
breathing -pnea
inflammation -itis
condition or disease -osis
deficiency -penia
disease -pathy
excessive flow -rrhag(e/ia)
mass, tumor -oma

Plural Forms

Adding an “s” or “es” to the end of a word is often the straightforward method to make a word plural in English and many modern Romance languages. In medical terminology, however, things are a little more complicated. The plural form of each word is based on the last two letters of the singular suffix.

There are several exceptions. For example, “virus” is a Latin term without a plural form. “Viruses” is the accepted plural form. Elsewhere, the suffix “s” or “es” occasionally prevails in common usage. For example, the plural form of “hematoma” is “hematomas” rather than “hematomata.”

Common singular endings and corresponding plural endings:

Plural Forms5
Singular Plural
a ae
en ina
ex, ix, yx ices
is es
ma mata
(a/i/y)nx (a/i/y)nges
um a
us i

Additional resources:

Related Guides:


  1. Banay GL. An Introduction to Medical Terminology I. Greek and Latin Derivations. Bulletin of the Medical Library Association. 1948;36(1):1–27.
  2. Wulff HR. The Language of Medicine. J R Soc Med. 2004;97(4):187–8.
  3. Ehrlich A, Schroeder CL. Introduction to Medical Terminology. 3rd ed. Delmar, Cengage Learning; 2014:5.
  4. Nath, JL, Lindsley KP. A Short Course in Medical Terminology. 4th ed. Philadelphia: Wolters Kluwer Health; 2018:38.
  5. Cohen BJ. Medical Terminology: An Illustrated Guide. 6th ed. Baltimore: Wolters Kluwer Health/Lippincott Williams & Wilkins; 2011. Tables 2–4.

Published: January 9, 2020

Last updated: March 22, 2023