Shelters housing 1000 vegetables (5)
I believe the answer is:
leeks
'vegetables' is the definition.
(leek is a kind of vegetable)
'shelters housing 1000' is the wordplay.
'shelters' becomes 'lees' (I've seen this in another clue).
'housing' means one lot of letters goes inside another.
'1000' becomes 'k' (synonyms).
'lees' enclosing 'k' is 'LEEKS'.
(Other definitions for leeks that I've seen before include "Welsh emblems" , "Welsh vegetables?" , "Emblems of 19" , "Scallions" , "Vichyssoise ingredient" .)