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.»