Starters of whelks in diner excellent, nice spread (5)

I believe the answer is:

widen

'spread' is the definition.
(thesaurus)

'starters of whelks in diner excellent nice' is the wordplay.
'starters of' indicates taking the first letters.
The initial letters of 'whelks in diner excellent nice' is 'WIDEN'.

(Other definitions for widen that I've seen before include "Stretch sideways" , "Increase dimension" , "Spread" , "Expand" , "Add" .)

I've seen this clue in The Independent.

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