malignant

adjective

ma·​lig·​nant mə-ˈlig-nənt 

1

: tending to produce death or deterioration

malignant malaria

especially : tending to infiltrate, metastasize, and terminate fatally

a malignant tumor

2

a

: evil in nature, influence, or effect : injurious

a powerful and malignant influence

b

: passionately and relentlessly malevolent : aggressively malicious

the malignant tongues of gossipers

c

obsolete : malcontent, disaffected

malignantly adverb

Synonyms of malignant

• malicious
• vicious
• cruel
• hateful
• nasty

Examples of malignant in a Sentence

a highly malignant form of cancer

a powerful and malignant influence

Recent Examples on the Web

The dogs learn how to identify the cancer by smelling three boxes, with one containing a sample of malignant blood. —Stephanie Stahl, CBS News, 30 Jan. 2026

And interferon-gamma is used against chronic granulomatous disease and a bone disease known as severe malignant osteopetrosis. —Bruce Y. Lee, Forbes.com, 24 Jan. 2026

Spark excelled in dark humor of a particular British type—apparently presentable people plotting ingeniously malignant crimes (think Roald Dahl)—and combined this with a gift for dry, demimondaine London dialogue in the style of, say, Anthony Powell. —The New Yorker, New Yorker, 14 Jan. 2026

According to his official death certificate obtained by PEOPLE, The Middle alum’s death was a result of malignant neoplasm of the bladder, better known as bladder cancer. —Liza Esquibias, PEOPLE, 8 Jan. 2026

Word History

Etymology

Late Latin malignant-, malignans, present participle of malignari

First Known Use

1542, in the meaning defined at sense 2c

Phrases Containing malignant

• malignant melanoma

Rhymes for malignant

• indignant
• nonmalignant
• premalignant

Kids Definition

malignant

adjective

ma·​lig·​nant mə-ˈlig-nənt 

1

: evil in influence or effect : injurious

2

: malicious sense 1

3

: tending to produce death

malignant tumors

malignantly adverb

Medical Definition

malignant

adjective

ma·​lig·​nant mə-ˈlig-nənt 

1

: tending to produce death or deterioration

malignant malaria

especially : tending to infiltrate, metastasize, and terminate fatally

malignant tumors

compare benign sense 1

2

: of unfavorable prognosis : not responding favorably to treatment

psychotic reactions with a malignant trend