Sharper knife's lost one time (5)
I believe the answer is:
cuter
'sharper' is the definition.
Both the definition and answer are comparative adjectives. Perhaps you can see an association between them that I can't see?
'knife's lost one time' is the wordplay.
'knife's' becomes 'cut' (I am not sure about this - if you are sure you should believe this answer much more).
'lost' suggests deleting specific letters.
'one' becomes 'a' (a thing is one thing).
'time' becomes 'era' (era is a kind of time).
'era' with 'a' taken out is 'er'.
'cut'+'er'='CUTER'
Can you help me to learn more?
(Other definitions for cuter that I've seen before include "Having raised appeal" , "More attractive" .)