Iota is typically used to refer to a tiny amount of something. Is there a letter antonym? Do you know of a case where iota and its antonym have been used in a quote to create a contrast.
(The first letter in Hebrew alphabet is aleph, and aleph-naught is used to refer to the first order of infinity in mathematics. But I have not heard of iota being used next to aleph.)
There is no one-letter antonym for iota. If you want an antonym with a similar Greek etymology, you could use plethora (many and varied) as an uncountable amount or myriad (ten thousand) for an indefinite large number of something.
I understand how your question arises. It is by comparison to alpha and omega, which are the first and last letters of the Greek alphabet. The alpha and the omega is a phrase meaning "the first and the last." The most famous use is in the Bible, when Jesus says, "I am the Alpha and the Omega".
Iota is used in another common expression: every jot and tittle. "Jot" refers to the vertical slash of letter iota, and "tittle" to the dot at the top. Every jot and tittle means "every tiny detail".
Iota comes from the Greek letter of the same name (ι), the tiniest of the letters in that alphabet (and a bit smaller than Latin i, since it lacks the tittle).
Consequently though, there's not really an antonym. Maybe -ι or 1/ι, but those would be mathematically speaking.
