1.nounSomething given beyond what is actually due; something added or superfluous.
2.nounSomething which occurs a fortiori, as a result of another effort without significant additional effort.
"Finally getting that cracked window fixed was a nice corollary of redoing the whole storefront."
3.nounA proposition which follows easily from the proof of another proposition.
"We have proven that this set is finite and well ordered; as a corollary, we now know that there is an order-preserving map from it to the natural numbers."