(law) A letter from a settlor to their trustees or a testator to their executors containing non-binding instructions.

plural of letter-box

An upper-case letter (A, B, C, ... as opposed to a, b, c, ...), used for emphasis, for starting sentences and proper names, etc.

(UK, dated, euphemistic) A condom.

(education) A letter of the alphabet assigned as an evaluation of schoolwork, with A generally being the best. Passing grades may also carry a plus or minus sign, with an A-minus (A-) better than B-plus (B+) and so on.

(linguistics) One of fourteen Arabic letters that do not affect the pronunciation of the "L" of a preceding definite article (ال- (al--)). The "L" in the Arabic definite article is pronounced "L" when followed by a moon letter: e.g., القُرْآن (al-qurʾān). The fourteen moon letters are: ء (ʾ), ب (b), ج (j), ح (ḥ), خ (ḵ), ع (ʿ), غ (ḡ), ف (f), ق (q), ك (k), م (m), ه (h), و (w), ي (y)

A letter that can be mailed successively to different recipients, with each recipient ostensibly (but sometimes sarcastically) being instructed in the body of the letter to mail the letter to another person or persons.

A power of attorney document.

(historical) The letter "A" in scarlet cloth required to be worn by those convicted of adultery in 17th-century Puritan New England.

A letter or written communication that serves to introduce an accompanying document; especially, a letter that introduces a résumé or curriculum vitae.