Everlasting cross inside or outside (8)
I believe the answer is:
external
'outside' is the definition.
(synonyms)
'everlasting cross inside' is the wordplay.
'everlasting' becomes 'eternal' (synonyms).
'cross' becomes 'x' (X is cross-shaped).
'inside' means one lot of letters goes inside another.
'eternal' placed around 'x' is 'EXTERNAL'.
'or' acts as a link.
(Other definitions for external that I've seen before include "Lying outside" , "Outer" , "Superficial" , "Outward" , "Relating to the outside" .)