(law) Rare form of letters patent (“a type of legal document in the form of an open letter issued by an authority granting a monopoly, right, status, or title to a person or organization”).

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 letter written to a newspaper, magazine or other periodical, usually intended for publication, about issues of concern to readers.

(linguistics) One of fourteen Arabic letters that cause the "L" of a preceding definite article اَل (al-) to be assimilated in pronunciation. The sun letter suppresses the sound of the "L" and then geminates: al + ṣīn = aṣ-ṣīn. The effect of the sun letter is limited to pronunciation and does not affect the spelling, except that a shadda may be written over the sun letter and in the fully vocalised spelling lām lacks any diacritics: الصِّين (aṣ-ṣīn). The fourteen sun letters are ت (t), ث (ṯ), د (d), ذ (ḏ), ر (r), ز (z), س (s), ش (š), ص (ṣ), ض (ḍ), ط (ṭ), ظ (ẓ), ل (l), ن (n). Phonetically, they represent coronal consonants.

(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)

(computing) An alphabetical identifier assigned to a drive or volume on MS-DOS or Windows.

Synonym of letter of comfort

(archaic) The letter r.

(US, law) A written agreement between a prosecutor and a defendant or prospective witness, allowing the latter to give the prosecutor information about an alleged crime, while limiting the prosecutor's ability to use that information against them.

plural of letter sheet