letter

a bread-and-butter letter: seebread-and-butter.

a dead letter: seedead.

the letter of the law the precise literal interpretation of a rule or instruction (as opposed to its broad intention).

a man (or woman) of letters a scholar or writer.

a red letter day: seered.

to the letter with adherence to every detail.

☞ The French equivalent of this phrase is au pied de la lettre, which has been used in English since the late 18th century.