Scores of eye movements in sleep (5,5)
I believe the answer is:
forty winks
'sleep' is the definition.
(thesaurus)
'scores of eye movements' is the wordplay.
'scores of' becomes 'forty' (a 'score' is twenty).
'eye movements' becomes 'winks'.
'forty'+'winks'='FORTY WINKS'
'in' acts as a link.
(Other definitions for forty winks that I've seen before include "Quick nap" , "Kip" , "Rest" , "Snooze" .)