Special long needle (5)
I believe the answer is:
spine
'needle' is the definition.
(thesaurus)
'special long' is the wordplay.
'special' becomes 'S' (common abbreviation as in Special Air Service).
'long' becomes 'pine' (to pine for someone is to long for them).
's'+'pine'='SPINE'
(Other definitions for spine that I've seen before include "Line of vertebrae" , "Backbone" , "Series of vertebrae" , "Thorn" , "Part of a book" .)