malignant neoplasm vs tumor

malignant neoplasm and tumor both are nouns.

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

As nouns, tumor is a hypernym of malignant neoplasm; that is, tumor 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
tumor: an abnormal new mass of tissue that serves no purpose

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

malignant neoplasm (noun)	tumor (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