Meaning

noun an annual phase of heightened sexual excitement in the males of certain large mammals (especially elephants); is associated with discharge from a gland between the eye and ear

originBorrowed from Hindustani (Hindi मस्त (mast) / Urdu مَسْت (mast, “drunk, intoxicated; lustful”); and also from Middle Hindi مَسْت (mst /⁠mast⁠/)), and from its etymon Classical Persian مَسْت (mast, “(adjective) drunk, intoxicated; (literary) in rut; of an elephant: in musth; (noun) drunkard”), ultimately from Proto-Indo-European *meh₂d- (“to be wet; to become wet”).

Etymology from Wiktionary, CC BY-SA 3.0