bilinear
adjective
°(mathematics of a function in two variables) Linear (preserving linear combination) in each variable.
"The function f(x,y)=xy is bilinear, because f(ax+bu,y)=a·f(x,y)+b·f(u,y) and f(x,ay+bv)=a⋅f(x,y)+b·f(x,v) for all values."