A young lion is called a cub. Adult males are called lions, while adult females are called lionesses. A lion transitions from cub to adult at 24 months in age.
The young of other big wild cats, including leopards and cheetahs, are also called cubs; however, smaller wild cats such as servals have young which are called kittens, much like the domestic cat. The word "cub" was first used for the young of foxes, and did not extend to the young of lions and other large predators until the 1590s. The original English word for the young of large predators, including lions, was "whelp."