Chereme
According to Wikipedia:
Cherology and chereme (from Ancient Greek: χείρ ‘hand’) are synonyms of phonology and phoneme which were previously used in the study of sign languages. The terms were coined in 1960 by William Stokoe at Gallaudet University, who sought to describe sign languages and their constituent parts as true and full languages. Once a controversial idea, the position is now universally accepted in linguistics. Stokoe's terminology, however, has been largely abandoned.
Cheremes, as the basic units of signed communication, are functionally and psychologically equivalent to phonemes in oral languages. Cherology, as the study of cheremes in language, is thus equivalent to phonology. These cher-root terms have thus been deprecated or replaced in the academic literature and elsewhere. Instead, the terms phonology and phoneme (or distinctive feature) are used, which in turn tends to stress the linguistic similarities between signed and spoken languages.
(Side note: That same Ancient Greek root is also related to other English words having to do with hands, such as chiropteran and chiropractor.)