How do I solve 5 across in Daily Telegraph Cryptic 3371?

Question

Accepted Answer

5 across reads "Wet blanket for Arctic swimmer?" (4,4 letters); the answer is COLD FISH. 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.

Wet blanket for Arctic swimmer? (4,4)

5A — Wet blanket for Arctic swimmer? (4,4) — COLD FISH