noun
accomplice; conspirator; cohort
Colloquial term for a partner in crime or someone in on a scheme together. Often used in the phrase ぐるになる (to be in cahoots).
あの二人はぐるになって私を騙したんだ。
Those two were in cahoots and tricked me.
彼は強盗のぐるだったことが判明した。
It turned out he was an accomplice in the robbery.
The origin is uncertain. It may be related to the verb 繰る (くる, to reel or wind), suggesting people bound together in a plot, but this is speculative.