Longman Dictionary of Contemporary English
Wiktionary
a. Constituting an epoch; opening a new era; introducing new conceptions or a new method in the treatment of a subject.
WordNet
adj. highly significant or important especially bringing about or marking the beginning of a new development or era; "epochal decisions made by Roosevelt and Churchill"; "an epoch-making discovery" [syn: epochal]
Usage examples of "epoch-making".
This brief and epoch-making book challenged conservative critical views about Jacobean theatre, and linked the plays much more closely with the political events of their era than previous critics had done.
Grownups have it in them to be creative, and sometimes, with the help of ambition, hard work, and a bit of luck they actually are, but being grownups, they have no sooner created some epoch-making invention than they become a slave to it.
If Ross had not received this intelligence, it is quite possible that the epoch-making geographical discoveries associated with his name would have been delayed for many years.
He helped himself at random - one name meant no more to him than mother - and went on to make an epoch-making discovery, that Wensleydale cheese and vintage port were a pair of heavenly twins, Castor and Pollux riding triumphantly as the climax of a glorious procession.
More trumpeters came next, splitting the ear with vehement outcries, and then several big brains, special correspondents one might well call them, or historiographers, charged with the task of observing and remembering every detail of this epoch-making interview.