on the spot—
1. at the place where one’s presence is needed:
- The police were on the spot very soon after the accident happened.
2. then and there; immediately:
- When Tom ruined an expensive machine, his boss fired him on the spot.
3. (coll.) in a difficult situation; in trouble (also: in a spot):
- He is on the spot because he cannot make a choice between Reagan and Nixon as the guest speaker.
spot on—(UK coll.) definitely right or true in one’s opinion, answer, etc.:
- “Is that the right answer, Sir?” “Yes, you’re spot on!”