A liquid food for infants (7)
I believe the answer is:
formula
'a liquid food for infants' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for formula that I've seen before include "Set form of words or method" , "One that's on track" , "Set of mathematical symbols or recipe" , "Liquid food for infants" , "Baby food" .)