All excited about cold drink of milk (7)
I believe the answer is:
lacteal
'of milk' is the definition.
(lacteal means relating to milk)
'all excited about cold drink' is the wordplay.
'excited' indicates an anagram.
'about' means one lot of letters goes inside another.
'cold' becomes 'C' (eg on taps).
'drink' becomes 'tea' (tea is a drink).
'all' anagrammed gives 'lal'.
'c'+'tea'='ctea'
'lal' going around 'ctea' is 'LACTEAL'.
(Other definitions for lacteal that I've seen before include "Milky resin" , "Milk-like; pertaining to milk" .)