Store mostly underwear in front of vacant repository (6)
I believe the answer is:
pantry
'store' is the definition.
(I've seen this before)
'mostly underwear in front of vacant repository' is the wordplay.
'mostly' means to remove the last letter (most but not all of the word).
'underwear' becomes 'pants' (underpants).
'in front of' is a charade indicator (letters next to each other) (some letters go in front of others).
'vacant repository' becomes 'ry' (I am not sure about this - if you are sure you should believe this answer much more).
'pants' with its last letter taken away is 'pant'.
'pant'+'ry'='PANTRY'
Can you help me to learn more?
(Other definitions for pantry that I've seen before include "Food store" , "Small storeroom for food etc" , "Small room or cupboard for storing food" , "Type of larder" , "Store cupboard" .)