on assignment

active unavailable working

buried employed engaged engrossed hustling occupied overloaded persevering slaving snowed swamped

already taken assiduous at it diligent having a full plate having enough on one's plate having fish to fry having many irons in the fire in a meeting in conference in someone else's possession in the field in the laboratory industrious on duty on the go tied-up up to one's ears with a customer

idle

inactive unoccupied

lazy quiet unbusy unemployed unengaged