squid
A slender cephalopod with tender, mild flesh, cooked either very briefly or for a long time.
This means squid, not cuttlefish or octopus. Whole fresh squid is sold by fishmongers and at larger supermarket fish counters, while frozen squid, whole or in rings, is widely available.
Substitute:
Cuttlefish is the best substitute, but its flesh is thicker and needs slightly longer cooking. Prawns or shrimp will do at a pinch, but they are sweeter and less chewy.