List with space is justifiable (7)
I believe the answer is:
tenable
'justifiable' is the definition.
(thesaurus)
'list with space' is the wordplay.
'list' becomes 'table' (I've seen this before).
'with' indicates putting letters inside.
'space' becomes 'en'.
'table' going around 'en' is 'TENABLE'.
'is' acts as a link.
(Other definitions for tenable that I've seen before include "okay as regards defence" , "fairly arguable" , "Believable" , "Can be maintained" , "Able to be held" .)