combining form 
noun Grammar
A form of a word normally used in compounds in combination with another element to form a word (e.g. Anglo- ‘English’ in Anglo-Irish, bio- ‘life’ in biology, -graphy ‘writing’ in biography).As an aside, telethon is one of those odd blends in which two combining forms, prefix and suffix, have been borrowed from separate words and jammed together, extinguishing any root word....
- That's why they're called Cryptoaliens, ‘crypto’ being a combining form that means ‘unknown’.
Usage
In this dictionary, combining form is used to denote an element that contributes to the particular sense of words (as with bio- and -graphy in biography), as distinct from a prefix or suffix that adjusts the sense of or determines the function of words (as with un-, -able, and -ation).