It’s mostly easy relaxing (6)
I believe the answer is:
siesta
'it's mostly easy relaxing' is the definition.
I can't judge whether this definition defines the answer.
'it's mostly easy relaxing' is the wordplay.
'mostly' means to remove the last letter (most but not all of the word).
'relaxing' is an anagram indicator.
'easy' with its final letter taken away is 'eas'.
'its'+'eas'='itseas'
'itseas' is an anagram of 'SIESTA'.
Can you help me to learn more?
(Other definitions for siesta that I've seen before include "Spanish afternoon activity" , "Daytime nap" , "Afternoon nap in Cadiz" , "Diurnal nap in Spain" , "rest of the Spaniards" .)