List having space is justifiable (7)
I believe the answer is:
tenable
'justifiable' is the definition.
(thesaurus)
'list having space' is the wordplay.
'list' becomes 'table' (list can mean a table or chart).
'having' is an insertion indicator.
'space' becomes 'en' (in printing, a space as wide as a letter 'n').
'table' going around 'en' is 'TENABLE'.
'is' is the link.
(Other definitions for tenable that I've seen before include "Believable" , "fairly arguable" , "possible to maintain" , "Able to be believed" , "Able to be held" .)