letter-card

[ let-er-kahrd ]
/ ˈlɛt ərˌkɑrd /

noun British.

a large postal card, with gummed edges, that can be folded lengthwise and sealed with the message inside.

Origin of letter-card

First recorded in 1890–95

British Dictionary definitions for letter card

letter card

noun

a card, usually one on which the postage is prepaid, that is sealed by being folded in half so that its gummed edges come into contact with each other
a long card consisting of a number of postcard views, with space for writing a letter on the backs, that is folded like a concertina for posting