How do I solve 24 across in Daily Telegraph Cryptic 3373?

Question

Accepted Answer

24 across reads "Rebuke – why?" (4,3 letters); the answer is WHAT FOR. It's a double-definition clue: two separate definitions of the same word sit side by side. No wordplay split and no indicators — both halves of the clue define the answer. The full step-by-step breakdown is on this page.

Rebuke – why? (4,3)

24A — Rebuke – why? (4,3) — WHAT FOR