Hoard remains under street (5)
I believe the answer is:
stash
'hoard' is the definition.
(I know that hoard can be written as stash)
'remains under street' is the wordplay.
'remains' becomes 'ash' (remains of a fire).
'under' is a charade indicator (letters next to each other) (below, in a down clue).
'street' becomes 'st' (abbreviation).
'ash' put after 'st' is 'STASH'.
(Other definitions for stash that I've seen before include "Stow away" , "Hide (something) away" , "Secret store (colloq.)" , "(Illegal) hoard" , "Cache" .)