From https://ncatlab.org/nlab/show/monoidal+category, a monoidal category requires a natural isomorphism
- a natural isomorphism $\lambda: (1 \otimes (-)) \rightarrow ^\cong (-)$ with components of the form $\lambda_x : 1 \otimes x \rightarrow x$
What does $(-)$ mean? Maybe the identity endofunctor? I suppose $(1 \otimes (-))$ is shorthand for a endofunctor which operates on objects by multiplying them by 1, but how does it operate on arrows?