Connection doesn't start as a crest (5)
I believe the answer is:
ridge
'a crest' is the definition.
(I've seen this before)
'connection doesn't start' is the wordplay.
'connection' becomes 'bridge' (bridge is a kind of connection).
'doesn't start' means to remove the first letter.
'bridge' with its initial letter taken away is 'RIDGE'.
'as' acts as a link.
(Other definitions for ridge that I've seen before include "Highland area" , "Raised edge" , "Top of a long narrow hill" , "Narrow raised strip as between hills" , "Raised strip between two furrows" .)