c.1374, from O.Fr.
moiste "damp," from V.L.
*muscidus "moldy," also "wet," from L.
mucidus "slimy, moldy, musty," from
mucus "slime" (see
mucus). Alternate etymology is from L.
musteus "fresh, green, new," lit. "like new wine," from
musteum "new wine" (see
must (n.1)). If this wasn't the source, it influenced the form of the other word in O.Fr.
Moisture is attested from 1366.