Crossword Genius

Collision is a sign of pregnancy (4)

Ross

I believe the answer is:

bump

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

I don't understand the rest of the clue.

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(Other definitions for bump that I've seen before include "Evidence of pregnancy - knock (into)" , "Collide - protuberance" , "Lump caused by a blow" , "Collide with force or violence" , "striking" .)

I've seen this clue in The Daily Express.
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