To be on tenterhooks is to be in a state of uncomfortable suspense. “She was on tenterhooks, waiting for the verdict.”
The phrase originated hundreds of years ago in the making of cloth; as Phrase Finder explains:
A tenter is a wooden frame, often in the form of a line of fencing, used to hang woollen or linen cloth to prevent it from shrinking as it dries. The tenterhooks are, not surprisingly, the hooks on the tenter used to hold the cloth in place.
The expression, however, is frequently misstated as “on tenderhooks,” as noted by both the Phrase Finder piece and this article in The Guardian on most frequently (in Britain) misquoted phrases. (Phrase Finder also recently addressed “damp squib;” It’s not an expression you hear that often on this side of the pond, and also, by the way, it’s not “damp squid,” although somehow that one’s more charming to me for its sheer nonsensicality.)
The tenterhooks/tenderhooks confusion is an eggcorn,* originally identified on Language Log and subsequently defined thus by the New Oxford American Dictionary:
a word or phrase that results from a mishearing or misinterpretation of another, an element of the original being substituted for one that sounds very similar or identical (e.g., tow the line instead of toe the line).
I’d be interested in reading a detailed analysis of eggcorns from a linguist; they depend on the mind’s ability to construct a reasonably credible alternate wording in place of the actual one. (For example, while serving time in purgatory with a corporate job, I used to have to read a lot of police accident reports, in which the actual traffic-law violation “failure to yield right of way” was quite often eggcorned (with a certain logic one can see) by investigating traffic officers into “failure to yield right away.” ) I’d guess that a phrase is particularly prone to being eggcorned if the phrase, like “on tenterhooks,” has long outlasted its origins (how many people have any idea what a “tenter” is?) and/or its actual, accurate meaning isn’t inherently obvious, and the word or phrase the mind swaps in is more common (“tender” vs “tenter”) and therefore, to the brain, somehow more credible, even if the resulting misquoted phrase doesn’t necessarily make any more (or possibly makes less) sense. Most of us, for example, don’t know what a “squib,” is but we do know what a squid is, and a squid certainly would be damp, ergo “damp squid.”
(If you’ve nothing pressing to do with your time, you can amuse yourself by browsing this database of eggcorns.)
To be (subtly, if you ask me) distinguished from the eggcorn is the mondegreen, what Grammar Girl calls “an error of the ear,” a misheard phrase or (often) lyric from a song that gets a new meaning from its mishearing. The term was coined by the writer Sylvia Wright in an article in Harper’s; she wrote of mishearing as “Lady Mondegreen” the last of these two lines (from a Scottish ballad**):
They hae slain the Earl of Murray,
And laid him on the green.
A line from Manfred Mann’s 1976 hit “Blinded by the Light” (a cover of a Bruce Springsteen song, who knew? ((I’m sure someone did, but I didn’t)) is one of the most famously misheard lyrics, perhaps because the actual lyric (“revved up like a deuce, another runner in the night”) doesn’t make any immediately obvious sense either. Though nothing takes the cake, so to speak, like the fully understandable and still incomprehensible lyrics from the Donna Summers hit “Macarthur Park.”
*update mea culpa. Long ago I identified “on tenterhooks” as a mondegreen. However, I have updated the post to outline the finer points of mishearing: an “eggcorn” is a misheard word or phrase, while a “mondegreen” is a misheard lyric or line from poetry (or, say, the U.S. Pledge of Allegiance***. GrammarGirl helpfully distinguishes mondegreens from malapropism from eggcorns from spoonerisms.
**update: typo “balland” corrected to “ballad.” Darn it, where’s a copyeditor when I need one? Oh…yeah…well…
***Required reciting of the Pledge of Allegiance, which was a daily ritual in my grade school, and which, I believe, continues today in many schools, now strikes me as vaguely creepy and totalitarian. I doubt that, mumbled by rote and often incomprehendingly, it has ever served to inspire any true patriotism (and what is true patriotism anyway?).
I also have an issue with playing “The Star Spangled Banner” before sporting events. What possible relevance does the song have to a bunch of kids running around a soccer field? (The fact that I take issue with this ritual every single time I encounter it, does, I’ll admit, remind me a bit of the New Yorker cartoon where a husband and wife are sitting amidst an audience full of laughing people, but the husband has a dour expression on his face, and his wife is querying, “Can’t you just for once forget that you’re a Concerned Scientist?”)