From over- +‎ confident.

• IPA^(key): /ˌəʊvə(ɹ)ˈkɒnfɪdənt/

• Audio (US):

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overconfident (comparative more overconfident, superlative most overconfident)

1. Too confident.

   Synonym: overweening

   Antonyms: underconfident, unconfident

   Coordinate terms: confident, self-assured

   • 2020 April 9, Gaby Hinsliff, “We used to moan about normal life, now our fear is we'll never get it back”, in The Guardian‎^[1]:

     The downturn triggered by putting everyday life on hold to halt the infection should, we were told, be V-shaped: a shock, but one from which we’d soon bounce back. Like many comforting predictions in the early days of this pandemic, that is beginning to look alarmingly over-confident.

   • 2021, Tom Eisenmann, Why Startups Fail, Crown, →ISBN, page 41:

     By propagating a "reality distortion field"—that is, mesmerizing potential employees, investors, and strategic partners so they focus on a startup's world-changing potential rather than on its real-world risks—overconfident and charismatic founders in particular are able to persuade people to commit resources under terms favorable to their new venture.

   1. (sometimes also, via understatement) Presumptuous, cocksure, rude, and disrespectful.

      Synonyms: overweening, arrogant

      Antonyms: underconfident, unconfident, meek, timid

      Near-synonyms: insolent, conceited, foolhardy, cocky