The term NOT IDLE is an antonym for being inactive or not doing anything. The crossword solutions for this term are ACTIVE (6 letters), BUSY (4 letters), MOVING (6 letters), INUSE (5 letters), INACTION (8 letters), and INDEFATIGABLE (13 letters). All of these words describe someone who is not idle, but instead is actively engaged in some activity. ACTIVE and BUSY both imply that someone is doing something, while MOVING implies that they are physically ACTIVE. INUSE and INACTION both suggest that someone is actively using something, while INDEFATIGABLE implies that someone is tireless and never gives up.