means Inclined to sudden or unpredictable shifts in temper, often toward gloom or irritability; given to spells of bad humor.

from From Old English 'modig,' built on 'mod' meaning mind, heart, spirit, or courage — the same 'mood' we still carry. Originally 'modig' could mean brave, proud, or high-spirited; the sense leaned over centuries away from noble fire and toward fickle gloom, so that what once described a bold heart now describes one that sulks. It's related to German 'Mut' (courage) and 'Gemüt' (disposition), kin from the shared Germanic root.