What does the cryptic crossword clue "Unnerves nearly defenceless slithery creature (11)" mean?

The wordplay uses a charade (building blocks). RATTLES (synonym="unnerves") + NAKE (synonym="NAKE") = RATTLESNAKE The answer is RATTLESNAKE.

Unnerves nearly defenceless slithery creature (11)

Guardian Cryptic #29124 | 25 Across | 2023-07-17 flower