dead center vs dead centre

dead center and dead centre both are nouns.

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

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

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

dead center (noun)	dead centre (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