Spread butter, with end of knife that's used to deliver liquid (7)
I believe the answer is:
burette
'that's used to deliver liquid' is the definition.
(type of glass tube used in chemistry)
'spread butter with end of knife' is the wordplay.
'spread' is an anagram indicator.
'with' means one lot of letters goes inside another.
'end of' suggests the final letters.
The final letter of 'knife' is 'e'.
'butter' with letters rearranged gives 'burtte'.
'burtte' going around 'e' is 'BURETTE'.
(Other definitions for burette that I've seen before include "Glass tube for measuring liquids" , "(Chem.) dispensing tube" , "Chemistry lab item" .)