Last traces of excess rain creep along and drop off (6)

I believe the answer is:

snooze

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'drop off' is the definition.
(I've seen this before)

I don't understand the rest of the clue.

(Other definitions for snooze that I've seen before include "Forty winks" , "Take a nap" , "Quick nap" , "Sleep lightly" , "A brief nap" .)

I've seen this clue in The Times.

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