This phrase is used to emphasize that someone has been completely deceived or tricked.
For example, ”he fell hook, line, and sinker for this year’s April Fool joke.”
Synonyms: completely, totally, utterly, entirely, wholly, absolutely, through and through, one hundred percent, ‘lock, stock, and barrel,’ without reservation, Full Monty.
Etymology: the phrase is based on the idea of a fish so hungry it swallows the hook (the part that catches the fish), the line ( the string) and the sinker (a lead weight attached to the line to keep it under water).
A fish may nibble at the bait, but when it takes the hook – and by association, the line and the sinker, it is well and truly caught.
The implication of this image from fishing is that the person who swallows a tale or an idea ‘hook, line and sinker’ is rather gullible, since the tale or idea may not stand up to hard scrutiny. This phrase originated in the United States about the middle of the 19th century, but a much older English phrase (“to swallow a gudgeon”) embodied the same idea.
Erle Stanley Gardner used it in The Case of the Stuttering Bishop. “A couple of private dicks that you don’t know anything about show up with a cock-and-bull story, and you swallow it hook, line, and sinker.”
Other than being the name of a rather funny British film, the “Full Monty” means the whole lot, everything available. The most probable origin hails from the Montague Burton tailors who established a shop in Chesterfield, England in 1904. They offered a complete outfit for hire (suit, shirt, tie, shoes, socks) and called it the “Full Monty” (from Montague). It’s ironic that this phrase is often now used to connote the opposite of a full suit of clothing.
If we’re fishing, we’re probably in a boat, right, mate? And so somebody says, “don’t rock the boat!” And that means ‘don’t upset people by trying to change a situation.’
But I would rather rock the boat than swallow something hook, line, and sinker! So I guess I’d better be a whale.