Cut-off trousers and vest are, surprisingly, items of great value (8,6)
I believe the answer is:
treasure troves
'items of great value' is the definition.
Although both the answer and definition are plural nouns, I can't see how one could define the other.
'cut-off trousers and vest are surprisingly' is the wordplay.
'cut off' means to remove the last letter.
'and' says to put letters next to each other.
'surprisingly' indicates an anagram (a surprising ordering of the letters).
'trousers' with its final letter taken off is 'trouser'.
'vest'+'are'='vestare'
'trouser' put after 'vestare' is 'vestaretrouser'.
'vestaretrouser' is an anagram of 'TREASURE TROVES'.
Can you help me to learn more?
(Another definition for treasure troves that I've seen is " cherished gatherings".)