Always the same outside, minus ten (7)
I believe the answer is:
eternal
'always' is the definition.
(I've seen this before)
'outside minus ten' is the wordplay.
'outside' becomes 'external' (similar in meaning).
'minus' is a deletion indicator.
'ten' becomes 'X' (Roman numeral).
'external' with 'x' removed is 'ETERNAL'.
'the same' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for eternal that I've seen before include "Forever and always" , "abiding" , "Imperishable" , "Forever or unchanging" , "Ceaseless" .)