Yearn to be the one in possession of the hot tip (4)
I believe the answer is:
ache
'yearn' is the definition.
(synonyms)
'the one in possession of the hot tip' is the wordplay.
'the one' becomes 'ace' ('ace' can be a synonym of 'one').
'in possession of' means one lot of letters goes inside another (has inside).
'tip' suggests taking the first letters (I've seen 'tips' mean this (tip can refer to the top end of something)).
The initial letter of 'hot' is 'h'.
'ace' enclosing 'h' is 'ACHE'.
'to be' acts as a link.
(Other definitions for ache that I've seen before include "Twinge" , "Play up" , "Dull steady pain" , "Take an aspirin for it" , "Hurt; yearn" .)