a word form that occurs only in compounds or derivatives, and that can combine with other such forms or with affixes to form a word (Ex.: bio- and -lysis in biolysis)
See combining form in American Heritage Dictionary 4
(kəm-bīˈnĭng)
noun
A modified form of an independent word that occurs only in combination with words, affixes, or other combining forms to form compounds or derivatives, as electro- (from electric) in electromagnet or geo- (from Greek geō-, from gē “earth”) in geochemistry.