canker

Concise Bible Dictionary:

The word of those who err from the truth eats like a “gangrene” which consumes the flesh. Such teaching saps the vitals of Christianity (2 Tim. 2:1717And their word will eat as doth a canker: of whom is Hymeneus and Philetus; (2 Timothy 2:17)).
 
Gangrene of the Lung

Strong’s Dictionary of Greek Words:

Number:
1044 (find all occurrences in KJV Bible)
Greek:
γάγγραινα
Transliteration:
gaggraina
Phonic:
gang’-grahee-nah
Meaning:
from γραίνω (to gnaw); an ulcer ("gangrene")
KJV Usage:
canker