Of milk (6)
'of milk' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for lactic that I've seen before include "Kind of acid" , "The acid in sour milk" , "The acid found in milk" , "Pertaining to milk" , "Derived from milk" .)
'of milk' is the definition.
(lacteal means relating to milk)
This is the entire clue.
(Other definitions for lacteal that I've seen before include "Milk-like; pertaining to milk" , "Milky resin" .)