Plant is absorbing intermittent rain (4)
I believe the answer is:
iris
'plant' is the definition.
'is absorbing intermittent rain' is the wordplay.
'absorbing' means one lot of letters goes inside another.
'intermittent' means one should take alternating letters.
The alternate letters of 'rain' are 'ri'.
'is' enclosing 'ri' is 'IRIS'.
(Other definitions for iris that I've seen before include "who keeps pupil in?" , "plant with showy flowers" , "pupil's governor" , "Pupil's place?" , "Part of the eye, usually brown or blue" .)