Five almost all identification logically sound (5)
I believe the answer is:
valid
'logically sound' is the definition.
(I've seen this in another clue)
'five almost all identification' is the wordplay.
'five' becomes 'V' (Roman numeral).
'almost' means to remove the last letter (most of the word but not all of it).
'identification' becomes 'ID' (abbreviation).
'all' with its last letter taken off is 'al'.
'v'+'al'+'id'='VALID'
(Other definitions for valid that I've seen before include "Legally acceptable, unexpired" , "Effective" , "Legally accepted or logical" , "Legally acceptable and sound" , "Legitimate" .)