Beach — nothing under cover? (4)
I believe the answer is:
lido
'beach' is the definition.
(thesaurus)
'nothing under cover?' is the wordplay.
'nothing' becomes 'O' (looks like zero - 0).
'under' says to put letters next to each other (below, in a down clue).
'cover?' becomes 'lid' (lid is a kind of cover).
'o' after 'lid' is 'LIDO'.
(Other definitions for lido that I've seen before include "Swim here" , "Italian bathing place" , "Public bathing beach" , "Outdoor swimming pool" , "bathing facilities" .)