Permanent cross removed from outside (7)
I believe the answer is:
'permanent' is the definition.
(similar in meaning)
'cross removed from outside' is the wordplay.
'cross' becomes 'x' (X is cross-shaped).
'removed from' is a deletion indicator.
'outside' becomes 'external' (synonyms).
'external' with 'x' removed is 'ETERNAL'.
(Other definitions for eternal that I've seen before include "abiding" , "non-stop" , "Undying" , "Everlasting, not affected by time" , "Seemingly without end" .)