Is more than one? (3)
I believe the answer is:
are
'is more than one?' is the definition.
(plural form of the verb 'is')
This is all the clue.
(Other definitions for are that I've seen before include "Is, in the plural" , "is for more than one" , "Exist; square measure" , "Unit of land measure equal to 100 square metres" , "(They/you/we) exist" .)