The Only Use

competent
in
To Kill a Mockingbird
(Edited)

It was mighty dark out there, black as ink. 'd take somebody mighty used to the dark to make a competent witness…
p. 315.7

competent = sufficiently capable

Definitions:

(1) (competent)
capable (able to do something in a generally satisfactory manner) -- sometimes specifically to have legal capability
(2) (meaning too rare to warrant focus)
In the field of law, competent has the specialized meaning of being legally qualified to do something such as to be mentally fit to make reasonable decisions; or to have jurisdiction or authority to take an action.

In classic literature, a competency can refer to having an income or assets to support living expenses.