First, let’s get one thing straight: you are on TENTERhooks, not TENDERhooks.
To be on tenterhooks is to be filled with painful or anxious anticipation or suspense, such as when you’re waiting for the result of an important medical test.
Where We Get the Word ‘Tenterhooks’
To figure out what a tenterhook is, we have to know that long ago manufacturers kept freshly milled woolen cloth from shrinking while it dried by stretching it on a wooden frame called a tenter. It comes from the Latin word tentus, which means “to stretch.”
The word ‘tenterhooks’ comes from the metal hooks that manufacturers used to stretch wool on a tenter while it dried.
The 1845 Encyclopaedia Metropolitana or Universal Dictionary of Knowledge, Volume 1, describes a tenter as “a number of vertical posts fixed to the ground, with a continuous horizontal fixed rail at the top as long as the piece of cloth; there are also other horizontal rails which are fitted between the upright posts … both the upper and lower rails are driven full of tenterhooks; on these the lists of the cloth are fastened, after which the lower or movable rail is pressed downwards to the full breadth of the cloth, and then secured in its place by the pins. In this state, the pieces are left to dry.”
So a tenterhook is a metal hook that holds the cloth in place on the tenter, and the frames were set out in fields so the wool could dry.
The Saturday Magazine, Volume 12 from 1838 describes the process like this:
“When the cloth first comes from the weaver, it is in a very rough unsightly state, and contains a quantity of oil … The next operation is ‘scouring,’ which is performed in the fulling-mill, the cloth being soaked in an alkaline ley and beaten by machinery; it is then well rinced with pure water and hung on the tenter-frames to dry.”
Maps Used to Show Tenter-Fields
According to Michael Quinion of the World Wide Words website, tenters were so numerous and common that old maps of England sometimes called out certain areas as tenter-fields.
In this literal sense, the earliest reference in the Oxford English Dictionary is from 1480, and the earliest full phrase I can read without butchering it is from 1518: Her nails as sharp as tenterhooks.
How ‘Tenterhooks’ Got Its Current Meaning
The figurative meaning seems to stem from the idea that the drying cloth is being strained and stretched by the tenterhooks, and by analogy, someone who is strained or stretched to wits’ end is on tenterhooks like the cloth. The first reference for this figurative sense is more than a couple hundred years later in 1748: I left him upon the tenterhooks of impatient uncertainty.
The OED says it is now a rare or obscure saying, but people also used to say they were “on tenters” or “on the tenter” to mean the same thing as “on tenterhooks.”
So remember, you aren’t on tenderhooks. You’re on tenterhooks.