Sharpens tip of lancet, to make true (6)
I believe the answer is:
honest
'true' is the definition.
(I know that true can be written as honest)
'sharpens tip of lancet' is the wordplay.
'sharpens' becomes 'hones' (honing is a kind of sharpening).
'tip of' suggests the final letters.
The final letter of 'lancet' is 't'.
'hones'+'t'='HONEST'
'to make' acts as a link.
(Other definitions for honest that I've seen before include "Honourable, true" , "Not lying" , "Genuine; fair" , "Not disposed to cheat" , "Open and truthful" .)