Term for each moon day (6)
I believe the answer is:
period
'term' is the definition.
(I've seen this before)
'each moon day' is the wordplay.
'each' becomes 'per'.
'moon' becomes 'io' (moon of Jupiter).
'day' becomes 'd'.
'per'+'io'+'d'='PERIOD'
'for' is the link.
(Other definitions for period that I've seen before include "term" , "Amount of time - US full stop" , "A portion of time" , "Stop in America" , "Time allocated for lesson in school" .)