What is the meaning of letters in idiom

You're asking about the meaning of letters in idioms, but it's not clear what you mean. Could you please clarify your question?

For example, are you asking about:

* Idioms with letters in them? Like "A stitch in time saves nine" or "Get your act together"?

* The meaning of letters within specific idioms? Like the "A" in "A stitch in time saves nine"?

* The meaning of letters as a concept in general in relation to idioms? Like how letters form words and words form idioms?

Once you clarify what you're asking, I can give you a more specific and helpful answer!