E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
To reject a candidate for literary honours because he is not up to the required mark. The rejected candidate is said to be plucked.
When degrees are conferred the name of each person is read out before he is presented to the Vice-Chancellor. The proctor used at one time to walk once up and down the room, and anyone who objected to the degree being conferred might signify his dissent by plucking or twitching the proctors gown. This was occasionally done by tradesmen to whom the candidate was in debt; but now all persons likely to be objected to, either by tradesmen or examiners, know it before-hand, and keep away. They are virtually plucked, but not really so.
A case of pluck. An instance of one who has been plucked: as Tom Jones is a case of pluck, i.e. is a plucked man.
A man of pluck. Of courage or spirit. The pluck is the heart, liver, and whatever else is plucked away from the chest of a sheep or hog. We also use the expressions bold heart, lily-livered, a man of another kidney, bowels of mercy, a vein of fun, it raised his bile, etc. (See LIVER.)