Pulsate in a bathrobe (5)
I believe the answer is:
throb
'pulsate' is the definition.
(I know that pulsate can be written as throb)
'in a bathrobe' is the wordplay.
'in' indicates a hidden word.
'THROB' is hidden in the letters of 'bathrobe'.
(Other definitions for throb that I've seen before include "beat repeatedly" , "Beat rhythmically" , "Pulsate; regular beat" , "Beat strongly" , "Have strong or irregular heartbeat" .)