Soldier or toper, possibly (7)
I believe the answer is:
trooper
'soldier' is the definition.
(trooper is a kind of soldier)
'or toper possibly' is the wordplay.
'possibly' indicates an anagram.
'or'+'toper'='ortoper'
'ortoper' is an anagram of 'TROOPER'.
(Other definitions for trooper that I've seen before include "Cavalry 21" , "Soldier, proverbial swearer" , "ship" , "Proverbially swearing soldier" , "Cavalry soldier" .)