malignant neoplasm vs tumour

malignant neoplasm and tumour both are nouns.

Word	Noun	Adjective	Verb	Adverb
malignant neoplasm	Yes	No	No	No
tumour	Yes	No	No	No

As nouns, tumour is a hypernym of malignant neoplasm; that is, tumour is a word with a broader meaning than malignant neoplasm:

malignant neoplasm: a tumor that is malignant and tends to spread to other parts of the body
tumour: an abnormal new mass of tissue that serves no purpose

Other hypernyms of malignant neoplasm include neoplasm, tumor, malignance, malignancy.

malignant neoplasm (noun)	tumour (noun)
a tumor that is malignant and tends to spread to other parts of the body	an abnormal new mass of tissue that serves no purpose