Green’s Dictionary of Slang

1. (also fish) suspect, dubious, unreliable, questionable; thus fishily adv.

1839		Punch XXXVI 82: The affair is decidedly fishy. However somebody must have the place, and so our friend Sam Warren takes the mastership, resigning his seat.
1849		De Bow Rev. VII 274: Any person should regard the story fishy and doubt the residence of so important a personage.
1855		T. Taylor Still Waters Run Deep II ii: Galvanics at two-and-a-half discount. That’s fishy!
1863		T. Taylor Ticket-Of-Leave Man Act III: Beautiful paper, most of it. One, two of ’em fishy. Well, I’ll try them three doors down.
1873		Sl. Dict. 162: Fishy doubtful, unsound, rotten; used to denote a suspicion of a ‘screw being loose,’ or ‘something rotten in the state of Denmark,’ in referring to any unsafe speculation.
1880		N.Z. Observer (Auckland) 25 Sept. 15/2: Albert Cellier [...] swears he wrote three of the principal airs in ‘Pinafore’. [Arthur] Sullivan has not answered the charge, which looks fishy.
1885		Bulletin (Sydney) 13 June 14/2: The mare was in the best of health on the previous night, but could hardly raise a gallop when brought on the course for the big event. [...] The business is generally regarded as ‘fishy.’.
1889		Nat. Police Gaz. (NY) 9 Nov. 6/3: Lieut. Henry Ward, chief of the Newark detective service, [...] thought the girl's story very fishy.
1895		Crowe Aus. Sl. Dict. 28: Fishy, something suspicious about it.
1896		Mirror of Life 12 Sept. 3/4: [I]t looks fishy when champion-of-the-world 'sullers want to claim a foul under circumstances as last Monday. It looks like chuck-chucking it.
1896		W.C. Gore Student Sl. in Cohen (1997) 11: fishy a. Of the nature of a fish-story; smacking of the incredible.
1904		Sun. Times (Perth) 3 Jan. 2/5: The betting certainly pointed to ‘fishy’ work in the race.
1907		Gem 16 Mar. 4: I can’t help thinking there’s something fishy about him.
1915		J. Buchan Thirty-Nine Steps (1930) 18: I had lied to Paddock about him, and the whole thing looked desperately fishy.
1923		Wodehouse Inimitable Jeeves 35: How can there have been anything fishy about this business?
1937		E. Garnett Family from One End Street 38: One lady went so far as to declare that, in her opinion, the whole business was ‘fishy’.
1948		(con. 1944) N. Mailer Naked and Dead 601: There was something fishy about this.
1959		C. Himes Crazy Kill 41: I knew there was something fishy about her coming to my church.
1967		(con. 1951) McAleer & Dickson Unit Pride (1981) 6: He gave me a fishy look but I deadpanned it.
1968		J. Hersey Algiers Motel Incident 332: Putting words in the police’s mouth – that weren’t nothing but a fishy trial.
1978		L. Kramer Faggots 280: For Abe of course smelled the something fishily off kilter.
1989		R. Dahl Rhyme Stew (1990) 23: The Rat said, ‘Ho! I do believe / There’s something fishy up your sleeve.’.
1991		R.G. Barrett Between the Devlin 118: [T]here was something else [...] he just couldn’t quite put his finger on. Something very fishy.
1999		Guardian Editor 11 June 14: With a reference to match-fixing [...] ‘it looks as if there is something fishy going on’.
2000		J.J. Connolly Layer Cake 61: I realise that the whole thing smells a little bit fish.
2006		C. Hiaasen Nature Girl 57: Her brother made up some fishy excuse.

2. (US) supercilious.

1919		Van Loan ‘The Bone Doctor’ in Score by Innings (2004) 370: He gave ’em the fishy handshake and the frozen eye.
2012		W.D. Myers Cruisers: A Star is Born 119: ]T]he man [...] asked if we were sure we had money for the cab fare. [...] We got to 31 East 32nd Street and told the guy in the lobby we had an appointment [...] He gave us the same fishy look the cabdriver did.