Etymology From Middle English gentilmanly; equivalent to gentleman + -ly (adjectival suffix).
1
Of, being, pertaining to, or resembling a gentleman or gentlemen.
Best of all, he ought to imagine his fellow-gamblers and the rest of the mob which stands trembling over a coin to be equally rich and gentlemanly with himself, and playing solely for recreation and pleasure.1867, Fyodor Dostoyevsky, chapter II, in The Gambler, translated by C. J. Hogarth^(https://en.wikisource.org/wiki/The_Gambler_(1867)/II):
With an election to cover and the soccer season in full swing, the sudoku newspaper rivalry stayed relatively gentlemanly until this month, when some of the last sudoku holdouts, including The Independent and The Guardian, joined the fray.2005 May 23, Eric Pfanner, “Puzzling phenomenon sweeps British papers”, in The New York Times, archived from the original on 28 Oct 2021:
2 more examples
Some schools bump up everyone’s grades, some just allow for more As and others all but eliminate the once-gentlemanly C.2010 June 22, Catherine Rampell, “In Law Schools, Grades Go Up, Just Like That”, in The New York Times, archived from the original on 24 Feb 2018, page A1:
The stationmaster was an important part of the local community. Anyon Kay, in his reminiscences of Horwich in the early 20th century, remembers a Mr Horsfield as stationmaster - "a gentlemanly character who took his job very seriously".2023 March 8, Paul Salveson, “Fond farewells to two final trains...”, in RAIL, number 978, page 54:
Etymology From Middle English gentilmanly; equivalent to gentleman + -ly (adverbial suffix).
1
In the manner or with the behavior of a gentleman; with social grace, politely.
He went gentlemanly dressed in East Virginia style, wore a high-top silk hat, as had lawyer Park, and sported a gold headed walking cane.1938, Charles A. Johnson, A Narrative History of Wise County, Virginia, page 165: