Definition of roach back in US English:

roach back

noun

  • In an animal: a back with a convex profile due to an arched spine. Occasionally as adjective: = roach-backed.

Origin

Mid 18th century; earliest use found in William Gibson (?1680–1750). Apparently from roach + back, after roach-backed.

Pronunciation

roach back

/ˈrəʊtʃ ˌbak/