Each operation has it's opposite. $1.\quad if\quad a+b=c,\quad then \quad c-b=a$ $2.\quad if\quad a\times b = c\quad then\quad c\div b = a$ $3.\quad if\quad 10^a = b\quad then\quad log(b) = a$ $4.\quad if\quad sin(\theta) = a\quad then\quad sin^{-1}(a) = \theta$ Therefore: $if\quad x^{\pi} = a\quad then\quad \sqrt [\pi]{a} = x$

So the answer is $\boxed {\sqrt [\pi]{y}}$