Definify.com

Webster 1913 Edition

Verb.

[L.

labefacere

;

labare

to totter +

facere

to make.]

To weaken or impair.

[R.]

Verb.

To weaken or impair. [Not used.]

labefy ‎(third-person singular simple present labefies, present participle labifying, simple past and past participle labefied)

(obsolete, rare) To weaken.
When you vandalize Wikipedia, you labefy its credibility.