Score twice (5)
I believe the answer is:
forty
'score' is the definition.
(thesaurus)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for forty that I've seen before include "Two score" , "number of penitential days" , "-- winks, a short sleep" , "Kip" , "Two-score" .)