Corollary. This term is seldom used but in mathematics. Its Greek
equivalent is πὁρισμα. The origin of the Latin term, which means a
little garland, in this sense is not very apparent. Anyhow the meaning
is familiar to everyone acquainted with Euclid—so familiar that one
cannot but wonder at Johnson's strange definition, "Corollary — A
conclusion, whether following necessarily from the premisses or not."
It really means a proposition necessarily resulting from a previous
demonstration, distinct from the conclusion of that, but yet to which
that is applicable, and no intermediate step requisite. Thus that every
equilateral triangle must be equiangular, is a corollary from the
conclusion of Prop. v. b. I. of Euclid. That is, that the angles at the
base of an isosceles triangle are equal, and any two angles of an
equilateral are angles at the base of an isosceles triangle.
The word corollary seems to have been formerly used in unscientific
language in the mere senses of redundancy or supplement.
Thus Shakespeare in the 'Tempest':
" Now come, my Ariel, bring a corollary
Rather than want a spirit."
And Dryden in the conclusion of the Preface to
his Fables, "as a corollary to this preface, in which I have done
justice to others, I owe somewhat to myself."