smell fishy, to

smell fishy

To seem suspicious of being improper, untoward, or duplicitous. A: "Their numbers don't match up with the taxes they've paid." B: "Hmm, something smells fishy." He thought Janet's response seemed a bit fishy, so he did a bit of investigation into her role in the company.
See also: fishy, smell
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.

smell fishy

to seem suspicious. Barlowe squinted a bit. Something smells fishy here, he thought. something about the deal smelled fishytoo good to be true.
See also: fishy, smell
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.

smell fishy

Be suspect or suspicious, as in His explanation definitely smells fishy; my guess is that he's lying. This idiom alludes to the fact that fresh fish have no odor but stale or rotten ones do. [Early 1800s]
See also: fishy, smell
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

smell fishy

in. to seem suspicious. (see also fishy.) Marlowe squinted a bit. Something smells fishy here, he thought.
See also: fishy, smell
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions Copyright © 2006 by The McGraw-Hill Companies, Inc. All rights reserved.

smell fishy, to

To be suspect. This term, which refers to the fact that fresh fish do not smell but stale or rotten ones do, has been around since the early nineteenth century. J. G. Holland explained it explicitly (Everyday Topics, 1876): “Fish is good, but fishy is always bad.” The metaphor turns up in James Payn’s Confidential Agent (1880): “His French is very fishy.”
See also: smell, to
The Dictionary of Clichés by Christine Ammer Copyright © 2013 by Christine Ammer
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References in periodicals archive ?
Tablets that contain chlorophyllin, a related synthetic compound, are given to people with colostomies, as well as those with an inherited disorder that makes their urine smell fishy, to reduce odor.