combining form
Meaning of combining form: The reason it is gastroenterology but gastritis: a linking vowel appears only when the next part starts with a consonant.
Definition of combining form
A combining form is a word root plus a linking vowel, written with a slash as gastr followed by o. The vowel, almost always o, exists only to make the term pronounceable when the next part begins with a consonant. It is dropped before a part that begins with a vowel, which is why the same root gives both gastroscopy and gastritis.
What is the linking vowel for?
Pronunciation, and nothing else. It carries no meaning of its own and changes nothing about the root it follows. Strings of consonants are hard to say, so a vowel is slipped in to break them up. Reference books print roots in this form, with the vowel shown after a slash, precisely because that is how the root behaves in most of the words built from it. The vowel is o in the great majority of medical terms, and an i appears in a small group of terms inherited from Latin rather than Greek.
When is the vowel kept and when is it dropped?
One rule covers almost every case: keep the vowel before a part beginning with a consonant, drop it before a part beginning with a vowel. That is the whole reason two terms from the same root can look so different.
| Root | What follows | Vowel | Result |
|---|---|---|---|
| arthr | itis, begins with a vowel | dropped | arthritis |
| arthr | algia, begins with a vowel | dropped | arthralgia |
| arthr | scopy, begins with a consonant | kept | arthroscopy |
| oste | porosis, begins with a consonant | kept | osteoporosis |
| gastr | enter, a second root | kept | gastroenterology |
Why does the rule change between two roots?
Because the vowel is kept between two roots whatever letter the second one starts with. Gastroenterology keeps its o even though the intestine root begins with a vowel, since dropping it would fuse the two roots into something unreadable. The same holds for osteoporosis and for terms such as arthralgia, where the ending rather than a second root follows. Names for specialists behave identically, so the gland root plus the ending for a practitioner yields endocrinologist, complete with its linking vowel.
Also known as
Used in a sentence
The combining form for the stomach appears with its linking vowel in gastroenterology.
Good to know
The linking vowel adds no meaning, so two terms from the same root differ only in spelling when one keeps the vowel and the other drops it before an ending that begins with a vowel.
Word origin
Where “combining form” comes from
The linking vowel o is the thematic vowel that joined the parts of Greek compounds, while Latin compounds used i for the same purpose, as in vermiform, meaning worm-shaped.