Vault over most of ice that’s hidden (7)
I believe the answer is:
cryptic
'hidden' is the definition.
(I've seen this before)
'vault over most of ice' is the wordplay.
'vault' becomes 'crypt' (I've seen this before**).
'over' is a charade indicator (letters next to each other).
'most of' means to remove the last letter.
'ice' with its last letter removed is 'ic'.
'crypt'+'ic'='CRYPTIC'
'that's' acts as a link.
(Other definitions for cryptic that I've seen before include "(Of crossword) withindirect clues" , "Obscure in meaning" , "Type of crossword clue (but not this one!)" , "Like some crosswords" , "Like our other puzzle" .)