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.

(historical) Referring to a type of musical notation used by Shakers, based on letters instead of notes. / (rare) Regarding letters of the alphabet.

(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.

(transitive) To print, inscribe, or paint letters on something. / (intransitive, US, scholastic) To earn a varsity letter (award).

(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.

A short, hand-written communication to thank someone who has recently provided the writer with hospitality, usually dinner or an overnight visit.