Obsolete form of letter.

plural of lettre

Alternative spelling of belles-lettres

(obsolete) The humanities. / (archaic) Literature, particularly light compositions valued for their aesthetic properties. / (archaic) Literary studies, particularly literary aesthetics.

man of letters, a literary man

(idiomatic) Before the term was coined (the term being a word or phrase used just previously in an anachronistic way)

(now historical) A warrant issued by the monarch in ancien régime France, especially one which imprisons someone without trial.

plural of lettre de cachet