A wealthy or married undergraduate of Cambridge, who pays extra
to “common” (i.e. dine) at the fellows' table. In Oxford, these
demi-dons are termed Gentlemen Commoners.
or gentleman commoner.
An empty bottle; so called because
these sort of students are, as a class, empty-headed
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894