monogram (n.)

"two or more letters intertwined," 1690s, from French monogramme or directly from Late Latin monogramma (5c.), from Late Greek monogrammon "a character formed of several letters in one design," especially in reference to the signature of the Byzantine emperors, noun use of neuter of monogrammos (adj.) "consisting of a single letter," literally "drawn with single lines," from Greek monos "single, alone" (from PIE root *men- (4) "small, isolated") + gramma "letter, line, that which is drawn or written" (see -gram). Earlier it meant "sketch or picture drawn in lines only, without shading or color," a sense also found in Latin and probably in Greek but now obsolete in English. Related: Monogrammatic.

"decorate with a monogram," 1856, from monogram (n.). Related: Monogrammed; monogramming.