Almost trustworthy, gets sharp (5)
I believe the answer is:
hones
'gets sharp' is the definition.
(I've seen this before)
'almost trustworthy' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'trustworthy' becomes 'honest' (associated in meaning).
'honest' with its last letter taken off is 'HONES'.
(Other definitions for hones that I've seen before include "Sharpens, like knife on stone" , "Perfects, sharpens" , "Sharpens as on whetstone" , "Sharpens on strap, say razor" , "gets sharp" .)