Yearn to have one hour in (4)
I believe the answer is:
ache
'yearn' is the definition.
('ache' can be a synonym of 'yearn')
'one hour in' is the wordplay.
'one' becomes 'ace' ('ace' can be a synonym of 'one').
'hour' becomes 'h'.
'in' means one lot of letters goes inside another.
'ace' placed around 'h' is 'ACHE'.
'to have' acts as a link.
(Other definitions for ache that I've seen before include "Dull prolonged pain" , "anguish" , "Feel pain" , "Twinge" , "Dull throbbing pain" .)