I'm taking a medical terminology class right now and I'm having issues discerning which word roots I'm supposed to use when they have the same meaning. For example, the combining forms pneum/o and pneumat/o both mean "lung" according to my textbook, however, a hernia of the lung is a "pneumat/o/cele" as opposed to "pneum/o/cele". I even googled these words up and only "pneumatocele" seems to be the proper term. A student in class asked the professor how we're supposed to know which word roots to use and the professor's reply was a bleak "you're just supposed to know". A lot of medical terms involves prefixes, suffixes and combining forms of similar definitions yet there must be some vague rule about knowing which parts to use with what. Another example, the suffixes "-ia" and "-osis" both mean "diseased condition" but a diseased lung is called "pneumon/ia" as opposed to "pneum/osis".

I'd REALLY appreciate any tips or forms of guidance with this. My professor is obviously very useless so I'm relying on this right now because I've googled for tips and tricks and can't find ANY.

  • Google for Medical dictionaries online.
    – rogermue
    Commented Mar 11, 2015 at 6:45
  • This really isn't about English, but about medical terminology. Sometimes words are changed based on sounds; the Latin prefix "con-" in front of a word starting with certain letters is changed to "com-", "in-" to "im-", etc. Pneumo comes from Greek for wind, pneumato- from the word for lung [(pneumōn, pneumon-), lung < πνεῦμα]. This is, again, not English. Commented Mar 11, 2015 at 6:54
  • Someone needs to edit away the rant against user's professor. Commented Mar 11, 2015 at 9:19
  • @medica: however jargony it is, medical terminology is still part of English.
    – herisson
    Commented Jun 16, 2015 at 7:06

4 Answers 4


The two are actually pneumon(o)- and pneumat(o)-. Pneumono- related to the lung, whereas pneumato- relates to the air or gas (usually contained in the lung). Pneumatocele is an air-filled cyst, whereas pneumonocele is a hernia of the lung.

If you look up the etymology for all of the suffixes and prefixes on the internet (from Wiktionary, for example), you'll be able to understand the subtle differences better.

  • Ah, hence the pneumatic drill and other air-aided appliances.
    – wys1wyg
    Commented Mar 11, 2015 at 4:51

For an exhaustive (and exhausting) list of affixes that will last you through your four years, try this wikipedia article:. It includes these two entries:

-osis: a condition, disease or increase

-i-asis: condition, formation, or presence of

Apparently '-ia' is added just to change the root into a noun - it isn't specifically medical and that may be why it's not in the Wikipedia article. Spelling shifts occur to make the terminology more palatable, adding an 'n' or dropping an 'o' between vowels, for example, just to complicate your life a little more.

Here is a simpler list from medworld:

Keep in mind that you'll get used to the terminology as you use it. You probably already know more than you think.

  • P.S. Use those pleurae and breathe!
    – wys1wyg
    Commented Mar 11, 2015 at 4:49
  • Thank-you for the link edits @ScotM. Where are the instructions do it your (better) way?
    – wys1wyg
    Commented Mar 11, 2015 at 5:03
  • Yes, -ia was a greek suffix that generally formed a noun of condition: parousia = nearness; diakonia = servitude; oikia = residence; etc. The medical connotation is derived.
    – ScotM
    Commented Mar 11, 2015 at 7:48

There are several good online dictionaries on medicine. Have a search with Google. The Free Dictionary has a Medical Dictionary. As I have seen in one article they have etymological notes.


The Gale Encyclopedia of Medicine is said to be one of the best dictionaries.


You can also use web-based flash cards to learn common medical suffixes and prefixes using https://medicalterminology.guide

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.