Both 'epoch-making' and 'epochal' constitute proper usage
The synonyms, epoch-making and epochal, are equally acceptable. Deciding when to use one word over the other will depend on the context. For example, if one wants to emphasize a development that defines an era, then epoch-making will probably convey that meaning more readily to a general audience than epochal, due to the two-part, hyphenated word construction.
Thus, if an individual reads:
- "Routine production of stone tools was an epoch-making advancement for hominins."
She might think to herself:
- "Ah, regular production of stone tools made the paleolithic epoch."
Both words, epoch-making and epochal, came into use during the mid-1800s.1 The OED notes that epoch-making was "orig. said chiefly of scientific discoveries or treatises; now extended to designate any remarkable or sensational event, publication, etc."2
I provide details below on the lesser-known word, epochal.
Detailed information regarding 'epochal'
Oxford English Dictionary
- Of the nature of an epoch; forming an epoch; epoch-making.3
Frequency (in current use): Frequency Band 4
Etymology (epoch): < late Latin epocha, < Greek ἐποχή stoppage, station, position (of a planet), fixed point of time, < ἐπέχειν to arrest, stop, take up a position, < ἐπί + ἔχειν to hold. Compare French époque, Italian epoca.
Examples of earliest use
1857 M. Pattison in Westm. Rev. Oct. 389 The..epochal crises of affairs.
1866 W. R. Alger Solitudes Nature & Man ii. 80 [David Hume's] place in the history of philosophy is of epochal importance.
1877 J. W. Dawson Origin of World vi. 127 Warring..has suggested that the Mosaic days are epochal days.
Oxford Dictionaries - English
epochal | ADJECTIVE
Forming or characterizing an epoch; epoch-making.4
‘the epochal scale of change in the East’
‘the beginning of Jesus's human life is an epochal event’
‘The current information revolution can be termed as the fifth epochal event since the birth of the human species.’
epochal - 1. 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"
- significant, important - important in effect or meaning; "a significant change in tax laws"; "a significant change in the Constitution"; "a significant contribution"; "significant details"; "statistically significant5
OED Online (n.d.). Oxford University Press. Retrieved July 19, 2017, from http://www.oed.com/view/Entry/63646
The above entry has not been updated for the OED 3rd ed., therefore it is drawn from the OED 2nd ed. (1989). The reference for the 2nd edition is:
Simpson, J. A., Weiner, E. S. C., & Oxford University Press. (1989). The Oxford English Dictionary. Oxford: Clarendon Press.
Oxford Dictionaries - English (n.d.). Retrieved July 19, 2017, from https://en.oxforddictionaries.com/definition/epochal.
epochal. (n.d.) WordNet 3.0, Farlex clipart collection. (2003-2008). Retrieved July 19 2017 from http://www.thefreedictionary.com/epochal
HT: @Ian for helping me remember the word. :0)