Two or more (6)
I believe the answer is:
plural
'two or more' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for plural that I've seen before include "Composed of more than one" , "More than one in number" , "More than one, not singular" , "Numbering more than one" , "Form of noun or verb in respect of more than one" .)