Comment: It's impugn:

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It's impugn:

im⋅pugn
/ɪmˈpyun/ [im-pyoon]

–verb (used with object)
1. to challenge as false (another's statements, motives, etc.); cast doubt upon.
2. Archaic. to assail (a person) by words or arguments; vilify.
3. Obsolete. to attack (a person) physically.
Origin:

New Hampshire and Ecuador.