benign tumour vs benign tumor

benign tumour and benign tumor both are nouns.

Word	Noun	Adjective	Verb	Adverb
benign tumour	Yes	No	No	No
benign tumor	Yes	No	No	No

As nouns, benign tumour and benign tumor are synonyms defined as:

Other synonyms of benign tumour include nonmalignant neoplasm, nonmalignant tumor, nonmalignant tumour.

benign tumour (noun)	benign tumor (noun)
a tumor that is not cancerous	a tumor that is not cancerous