Given a $\mathbb{S}$-module, we can construct a Schur functor, which is an endo functor in the category of vectorspaces. But given a Schur functor, how can we get back the $\mathbb{S}$-module? In Loday/Vallette's book on Operads, they say that if $P$ is the Schur functor, look at $P(V)$, where $V$ is an $n$-dimensional vectorspace. The $n$-multilinear part of $P(V)$ is isomorphic to $P(n)$, as an $S_n$-module. Can someone explain what is meant by the 'multilinear part'?