Clean off tip of the knife (6)
I believe the answer is:
lancet
'knife' is the definition.
(I know that lancet is a type of knife)
'clean off tip of the' is the wordplay.
I cannot really understand how this works, but
an anagram of 'clean' is 'lance' which is within the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found within the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for lancet that I've seen before include "Medical journal; window opening" , "Theatrical knife" , "Pointed two-edged knife used by surgeon" , "Surgical knife with a pointed double-edged blade: pointed Gothic arch" , "Surgical tool" .)