Widow may have one quick look when speaking (4)
I believe the answer is:
'widow may have one' is the definition.
(as in a widow's peak, type of hairline)
'quick look when speaking' is the wordplay.
'quick look' becomes 'peek' (I've seen this before).
'when speaking' shows a homophone (sound like).
'peek' sounds like 'PEAK'.
(Other definitions for peak that I've seen before include "Reach the highest point" , "Pinnacle" , "Sharp pointed summit" , "Tip" , "Part of cap; mountain" .)