Undermine
Definition 1 of 2

Subtle Weakening
Undermine suggests a gradual process, not an immediate effect.

His jokes about her work began to slowly undermine her motivation.
Hidden Motives
Actions that undermine often appear harmless at first.

Smiling, he shared the team's plans with the rival, aiming to undermine their success.
Connotation of Betrayal
Undermine can imply betrayal, as trust is broken.

By spreading rumors, she began to undermine his reputation among his friends.
Compare with
belittlecorrodedebasedisparageerodesabotslandersubvertweaken
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