Probably from Late Latin medietās, medietātem (from Latin medius), through an intermediate Vulgar Latin root *diemitatem through metathesis or from dimidietās, dimidietātem. (Compare Portuguese metade). The first element of the word may be linked to or influenced by an Albanian term (cf. gjysmë), while the latter part follows the normal derivation from Latin -itas, -itatem endings; the final result may have occurred due to a crossing of the initial part with the Latin word.
An alternative theory suggests an enlargement of dialectal jumate (cf. Aromanian giumate, giumitate), from Proto-Albanian *jūmatjā (cf. modern gjysmë, dialectal gjymës, gjymësë). The phonetic transition between the two is unclear, however, and makes this etymology somewhat less likely.