IMO Functions are pure raw forms of one whole thing, that describes its base and also the 'little things' it's all about, all in one word. Such as:
Ni: Pure Idea
Ne: Pure Persuasion
Ti: Pure Process
Te: Pure Action
Fe: Pure Emotion
Fi: Pure Relationship
Se: Pure Essence
Si: Pure Harmony (ew don't like this one but can't think of a better word)