Both Uses

discredit
in
A Sketch of the Past
(Auto-generated)

For it was agreed that it wasn't the poor Maude girls' fault—the handsome dark girls who lived behind the locked gate, scaring duns, were to be pitied for their disreputable parents' discreditable imprisoned lives.†
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discreditable = tending to damage the reputation of

standard suffix: The suffix "-able" means able to be. This is the same pattern you see in words like breakable, understandable, and comfortable.
To my discredit, I never wore it again in George's presence.†

discredit = damage the reputation of

Definitions:

(1) (discredit)
damage the reputation of -- often causing distrust of or disbelief in
(2) (meaning too rare to warrant focus)