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College Resource Center : Health Careers : Medical Assisting Study Aids : Combining Word Parts

Combining Word Parts

Some terms are simply the root words (or combining forms) by themselves, while others consist of multiple roots, a prefix, and one or more suffixes. The following word constructions illustrate the standard four ways to combine word parts into terms:

  1. root word (or combining form)
    Example: phleb = vein
  2. root word (or combining form) + additional combining form
    Example: thrombophleb = clot in a vein
  3. root word (or combining form) + additional combining form + suffix
    Example: thrombophlebitis = inflammation of a vein with clotting
  4. prefix + root word (or combining form) + additional combining form + suffix
    Example: post-thrombophlebitis = after inflammation of a vein with clotting (recovery)

Exceptions to the Rules

As with most languages, there are exceptions to the rules describing how medical terms are formed. Being aware of them will help you determine the meanings of words that seem to stray from the typical patterns. For example, terms consisting of a root word and a suffix usually require a combining vowel between the two word parts. However, this is a general rule and there are some exceptions, such as terms in which the suffix begins with a vowel, as in cardiectomy.

In addition, the combining vowel--and the final vowel in a root--are both dropped before a suffix that begins with a vowel, as in carditis. If the suffix begins with a consonant, the combining vowel is usually retained. Combining vowels are not used between a prefix and a root word. Remember that not all medical terms have combining vowels.


Some suffixes in medical terminology are technically compound suffixes--that is, one suffix with a second suffix added on. These suffixes are often found in terms relating to medical specialties, diagnoses, or procedures. The second suffix is usually only one letter. It may simply function as a noun marker (a visual sign that the word is a noun), as in

erythrocyte (erythr/o + -cyt + -e), a red blood cell
erythr/o = red     +     -cyt = cell     +     -e = noun marker

In the following example, part of the suffix is another single letter, a y:

urology (ur/o + -log + -y), the process of knowing urinary function and disease
ur/o = urine or urinary tract  +  -log = to know (derived from Greek word "logos")  +  -y = condition or process of

An analysis of the word urology points out a practice that occurs frequently in the formation of medical words. When two suffixes are combined, the resulting meaning is usually a shortened version of the two separate suffix meanings. Thus, -logy becomes "the study of" (a shortened version of "the process of knowing"). You will encounter many of these compound suffixes and usually learn the combined meaning.

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