What does the cryptic crossword clue "Murder composer that’s challenging, cold and dangerous (7)" mean?

The wordplay uses a charade (building blocks). ICE (synonym="slang for “Murder”") + BERG (synonym="BERG") = ICEBERG The answer is ICEBERG.

Murder composer that’s challenging, cold and dangerous (7)

Guardian Cryptic #29376 | 13 Across | 2024-05-07 flower