is a specific kind of: benefactor, helper.

derivation: ameliorate, amend, better, improve, meliorate | benefit, do good.

is a specific kind of: component, constituent, element.

is a broader term that covers: additive | afterthought | annex, annexe, extension, wing | attachment | elongation, extension.

derivation: add on | ameliorate, amend, better, improve, meliorate | add, bestow, bring, contribute, impart, lend.