1) Admirable 2) Brilliant 3) Conspicuous 4) Continuing in existence 5) Excellent 6) Exceptional 7) Extraordinary 8) First-rate 9) In arrears 10) Incomparable 11) Not yet completed 12) Owed as a debt 13) Prominent 14) Remaining 15) Special 16) Still to pay 17) Superb 18) Superior 19) Tremendous 20) Unsettled Found on https://www.crosswordclues.com/clue/outstanding
Out·stand'ing adjective That stands out; undischarged; uncollected; not paid; as, outstanding obligations. « Revenues . . . as well outstanding as collected.» A. Hamilton. Found on http://www.encyclo.co.uk/webster/O/47
adjective of major significance or importance; `a great work of art`; `Einstein was one of the outstanding figures of the 20th centurey` Found on https://www.encyclo.co.uk/local/20974
prominent; conspicuous; striking: an outstanding example of courage. · marked by superiority or distinction; excellent; distinguished: an outstanding student. · continuing in existence; remaining unsettled, unpaid, etc.: outstanding debts. · (of securities and the like) publicly issued and sold or in circulation. · standing out;... Found on https://www.infoplease.com/dictionary/outstanding