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[as-er-teyn] /ˌæs ərˈteɪn/
verb (used with object)
to find out definitely; learn with certainty or assurance; determine:
to ascertain the facts.
Archaic. to make certain, clear, or definitely known.
Origin of ascertain
1400-50; late Middle English, variant of assertain, acertain < Middle French acertain- (tonic stem of acertener to make certain), equivalent to a- a-5 + certain certain
Related forms
ascertainable, adjective
ascertainably, adverb
ascertainer, noun
ascertainment, noun
nonascertainable, adjective
nonascertainableness, noun
nonascertainably, adverb
nonascertainment, noun
preascertain, verb (used with object)
preascertainment, noun
unascertainable, adjective
unascertainably, adverb
unascertained, adjective
well-ascertained, adjective
Synonym Study
1. See learn. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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Examples from the Web for unascertainable
Historical Examples
  • There was first the Procession of the Maestranza, of unascertainable antiquity.

    Diversions in Sicily H. Festing Jones
  • Antonyms: unknowable, unascertainable, incognoscible, unrecognizable.

    Putnam's Word Book Louis A. Flemming
  • The composition of the earliest inks has not yet been obtained and, likely, is unascertainable.

    The Reign of the Manuscript Perry Wayland Sinks
  • During the seventh century many sanguinary battles were fought, the sites of which are now unascertainable.

  • The exact date of his advent to that place seems to be unascertainable, but it was more than fifty years ago.

    The Old Pike Thomas B. Searight
  • Its exact amount is unascertainable, for neither Government kept adequate statistics before 1820.

  • The back yard is unfenced, and extends to the sky-line and an unascertainable bit beyond.

    The Faith of Men Jack London
  • The German losses were, of course, unascertainable, but they were undoubtedly very much higher than ours.

    The First Seven Divisions Ernest W. Hamilton
British Dictionary definitions for unascertainable


verb (transitive)
to determine or discover definitely
(archaic) to make certain
Derived Forms
ascertainable, adjective
ascertainably, adverb
ascertainment, noun
Word Origin
C15: from Old French acertener to make certain
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for unascertainable



early 15c., "to inform, to give assurance," from Anglo-French acerteiner, Old French acertener "to assure, certify" (13c.), from a "to" (see ad-) + certain "certain" (see certain). Modern meaning of "find out for sure by experiment or investigation" is first attested 1794. Related: Ascertained; ascertaining.

Online Etymology Dictionary, © 2010 Douglas Harper
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