The vector parts that add up to the resultant are called

"Components"

Explanation:

A vector pointing in a particular direction can always be decomposed into multiple vectors whose sum yields that vector. These vectors are referred to as components. Most frequently, vectors are decomposed into its components in the context of coordinate systems. For example an origin vector of length sqrt(2) pointing up 45 degrees in a (x,y) coordinate system has an x-component (1,0) and a y-component (0,1).