Different, not the same (5)
I believe the answer is:
other
I believe this is a double definition.
'different' is the first definition.
(similar in meaning)
'not the same' is the second definition.
(I've seen this before)
(Other definitions for other that I've seen before include "Throe (anag)" , "Alternate; additional" , "Different, alternative" , "Different (from those mentioned)" , "One may be significant" .)