Keep in date, possibly (6)
I believe the answer is:
detain
'keep' is the definition.
(thesaurus)
'in date possibly' is the wordplay.
'possibly' indicates an anagram.
'in'+'date'='indate'
'indate' is an anagram of 'DETAIN'.
(Other definitions for detain that I've seen before include "Hold in detention" , "Delay, arrest" , "Imprison" , "Hold back - arrest" , "Stop" .)