Inexperienced peacekeepers put to the test (7)
I believe the answer is:
untried
'inexperienced' is the definition.
(similar in meaning)
'peacekeepers put to the test' is the wordplay.
'peacekeepers' becomes 'un'.
'put to the test' becomes 'tried' (I've seen this in another clue).
'un'+'tried'='UNTRIED'
(Other definitions for untried that I've seen before include "novel" , "not yet proved reliable" , "escape court appearance thus" , "Intrude (anag.)" , "Yet to be taken to court" .)