Call for some buttermilk (4)
I believe the answer is:
term
'call' is the definition.
(to term something is to call it something)
'some buttermilk' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'TERM' is hidden in the letters of 'buttermilk'.
'for' is the link.
(Other definitions for term that I've seen before include "Limit - school time" , "Spell - word" , "Period of school life" , "what being 9 [PREGNANT] leads to?" , "Fixed period of time" .)