Head north with oxygen, finally lifting spirit (6)
I believe the answer is:
noggin
'head' is the definition.
(noggin is a kind of head)
'north with oxygen finally lifting spirit' is the wordplay.
'north' becomes 'n' (synonyms).
'with' is a charade indicator (letters next to each other).
'oxygen' becomes 'o' (atomic symbol for oxygen).
'finally' says to take the final letters.
'spirit' becomes 'gin' (alcoholic spirit).
The last letter of 'lifting' is 'g'.
'n'+'o'+'g'+'gin'='NOGGIN'
(Other definitions for noggin that I've seen before include "Human head -- small drink" , "Small amount of alcohol" , "spirited measure" , "Small measure of alcohol, about 1/4 pint" , "Small measure of liquid" .)