Green is one with secure seat (7)
I believe the answer is:
beanbag
'seat' is the definition.
(I've seen this before)
'green is one with secure' is the wordplay.
'green' becomes 'be' (I can't justify this - if you can you should give a lot more credence to this answer).
'is one' becomes 'an' (an apple is one apple).
'with' says to put letters next to each other.
'secure' becomes 'bag' (bag can mean to secure).
'be'+'an'+'bag'='BEANBAG'
(Other definitions for beanbag that I've seen before include "comfortable seat" , "Small cloth sack filled with dried pulses, used in games" , "Large cushion used as a seat" , "somewhere comfy to sit" , "Granule filled sack for lounging on" .)