How do I solve 13 across in Daily Telegraph Cryptic 3371?

Question

Accepted Answer

13 across reads "Idle brain" (4 letters); the answer is LOAF. 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.

Idle brain (4)

13A — Idle brain (4) — LOAF