unforgettable

From un- +‎ forget +‎ -able or un- +‎ forgettable.

• IPA^(key): /ˌʌnfə(ɹ)ˈɡɛtəbəl/

• Audio (Southern England):

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• Rhymes: -ɛtəbəl

unforgettable (comparative more unforgettable, superlative most unforgettable)

1. Very difficult or impossible to forget.

   Synonyms: memorable; see also Thesaurus:memorable

   Antonym: forgettable

   The things he subjected me to were horrible and unforgettable.

   • 1903 July, Jack London, “The Law of Club and Fang”, in The Call of the Wild, New York, N.Y.: The Macmillan Company; London: Macmillan & Co., →OCLC, page 44:

     He had never seen dogs fight as these wolfish creatures fought, and his first experience taught him an unforgetable lesson. It is true, it was a vicarious experience, else he would not have lived to profit by it.

   • 1961 July, J. Geoffrey Todd, “Impressions of railroading in the United States: Part Two”, in Trains Illustrated, page 419:

     The leading engine was one of the Class Y6 2-8-8-2 compound articulateds, [...] The stack noise of one of these great brutes slogging up a grade was quite unforgettable.