dead centre vs dead center

dead centre and dead center both are nouns.

Word	Noun	Adjective	Verb	Adverb
dead centre	Yes	No	No	No
dead center	Yes	No	No	No

As nouns, dead centre and dead center are synonyms defined as:

dead centre and dead center: the position of a crank when it is in line with the connecting rod and not exerting torque

dead centre (noun)	dead center (noun)
the position of a crank when it is in line with the connecting rod and not exerting torque	the position of a crank when it is in line with the connecting rod and not exerting torque