Maybe a summer snake? (5)

I believe the answer is:

adder

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'snake?' is the definition.
(adder is a kind of snake)

I can't explain the remainder of the clue.

(Other definitions for adder that I've seen before include "danger in the countryside" , "Venomous sort" , "Totter" , "Snake (like an abacus?)" , "Mathematical reptile" .)

I've seen this clue in The Sun.

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