High Quality Content by WIKIPEDIA articles! In morpheme-based morphology, a null morpheme is a morpheme that is realized by a phonologically null affix (an empty string of phonological segments). In simpler terms, a null morpheme is an "invisible" affix. It's also called zero morpheme; the process of adding a null morpheme is called null affixation, null derivation or zero derivation. The concept was first used over two thousand years ago by P??ini in his Sanskrit grammar. Some linguists[who?] object to the notion of a null morpheme, arguing that it sets up an unverifiable distinction between a "null" or "zero" element, and nothing at all.