labour pains vs labor pains

labour pains and labor pains both are nouns.

Word	Noun	Adjective	Verb	Adverb
labour pains	Yes	No	No	No
labor pains	Yes	No	No	No

As nouns, labour pains and labor pains are synonyms defined as:

labour pains and labor pains: a regularly recurrent spasm of pain that is characteristic of childbirth

Other synonyms of labour pains include birth pangs.

labour pains (noun)	labor pains (noun)
a regularly recurrent spasm of pain that is characteristic of childbirth	a regularly recurrent spasm of pain that is characteristic of childbirth