1
medical
: very serious and dangerous : tending or likely to grow and spread in a rapid and uncontrolled way that can cause death
a malignant [=cancerous] tumor/growth
a highly malignant form of cancer
2
formal
: very evil
a powerful and malignant influence
Cite this Entry
“Malignant.” Merriam-Webster.com Simple Definition, Merriam-Webster, https://www.merriam-webster.com/simple/malignant. Accessed 17 Apr. 2026.
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