Lots sleep on ends of nails (6)
I believe the answer is:
dozens
'lots' is the definition.
(synonyms)
'sleep on ends of nails' is the wordplay.
'sleep' becomes 'doze' (doze means to sleep).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'ends of' says to hollow out the word (remove centre letters).
'nails' with its middle taken out is 'ns'.
'doze'+'ns'='DOZENS'
(Other definitions for dozens that I've seen before include "Large numbers" , "Sets of twelve" .)