The acklay was a spidery buggy monster with a thick exoskeleton, sharp fangs, the jaws that bite and the claws that catch. It was also Pig Latin for "lack." Among the things the acklay lacked were: intelligence, self-awareness, opposable digits, and social hierarchy. They were kidnapped from wild places like Felucia and fought in arenas, like the one on Geonosis. Obi-Wan Kenobi (not Pig Latin) killed one, but it took some effort.
The creature is in no way related to the slang "ack-lay," i.e., the act of having sex with Cathy, nor did it have anything to do with Lewis Carroll's Jabberwock.