Morphology - Unit Two - Lesson No. 10
A subtractive morpheme (or disfix) is a morpheme that manifests itself through elision (deletion of some segments from the root or stem). Thus it can be seen as an instance of anti-affix, i.e. functioning as just the opposite of affixation. Whereas affixation requires addition to the stem or root in some way, subtractive morpheme requires subtracting some segments (derivational or inflectional) from the root or stem.
French is famous for exhibiting subtractive morphemes. For instance, plural forms are derived from their singular forms; many masculine from the feminine forms, by deleting the final consonant and making a change to the vowel, which can be generally predicted in most cases.