Someone who cranks something, or something that operates by cranking; also slang for an excellent or outstanding person or thing.
From crank + -er (agent suffix indicating a person who does something). The slang sense developed in 20th-century informal English to mean 'excellent.'
A 'cranker' wave in surfing means a great big one—the term likely comes from the cranking motion surfers make while riding, and it stuck as surfer slang for anything exceptional.
Complete word intelligence in one call. Free tier — 50 lookups/day.