noun
: a linguistic form that occurs only in compounds or derivatives and can be distinguished descriptively from an affix by its ability to occur as one immediate constituent of a form whose only other immediate constituent is an affix (as cephal- in cephalic ) or by its being an allomorph of a morpheme that has another allomorph that may occur alone (as electro- representing electric in electromagnet, resini- representing resin in resiniferous, forma- representing formaldehyde in formalith, para- representing parachute in paratrooper ) or can be distinguished historically from an affix by the fact that it is borrowed from another language in which it is descriptively a word (as French mal giving English mal- in malodorous ) or a combining form (as Greek kako-, combining form of kakos, giving English caco- in cacography )