From un- +‎ accountable.

• IPA^(key): /ˌʌnəˈkaʊntəbl̩/

• Audio (US):

  (file)

• Hyphenation: un‧ac‧count‧a‧ble

unaccountable (comparative more unaccountable, superlative most unaccountable)

1. Inexplicable; unable to be accounted for or explained.
   • 1852, Herman Melville, Pierre; or The Ambiguities:

     And the having individually entertained four such resolves, without perceiving that once brought together, they all mutually expire; this, this ineffable folly, Pierre, brands thee in the forehead for an unaccountable infatuate!

   • 1920, Agatha Christie, The Mysterious Affair at Styles, London: Pan Books, published 1954, page 134:

     If only Poirot had been accessible, I could have asked his advice. What possessed him to go posting off to London in this unaccountable way?

2. Not responsible; free from accountability or control.
   • 2017 March 1, “UN slams Thai 'culture of torture'”, in Bangkok Post‎:

     Thailand has dropped legislation to criminalise torture and disappearances after years of working on the bill, the United Nations human rights office said on Tuesday, leaving state employees unaccountable for serious crimes.

   • 2021 May 5, Tony Streeter, “Network News: Disused structures "assets to be preserved", say MPs”, in RAIL, number 930, page 23:

     Graeme Bickerdike, a member of campaign organisation The HRE Group, told RAIL: "This infilling and demolition programme - costing much more than repair - has been conceived with no thought for its impact beyond the silos where distant, unaccountable officials manage their spreadsheets.

• “unaccountable”, in Lexico, Dictionary.com; Oxford University Press, 2019–2022.