Relaxation from brainteasers (4)
I believe the answer is:
ease
'relaxation' is the definition.
(synonyms)
'from brainteasers' is the wordplay.
'from' indicates the answer is hidden within the clue.
'EASE' can be found hidden inside 'brainteasers'.
(Other definitions for ease that I've seen before include "Leisure, comfort" , "State of relaxation or rest" , "Effortlessness" , "Allay" , "Comfort; simplicity" .)