Impulsion Vs Compulsion

This is something I've been wondering for a while so I'd better figure it out. I keep wondering what the difference is between an impulsion and a compulsion.

 im·pul·sion  (ĭm-pŭl′shən)

n.

1. The act of impelling or the condition of being impelled: "I do not move . . . unless it be under the impulsion of a third party" (Samuel Beckett).

2. An impelling force; a thrust.

3. Motion produced by an impelling force; momentum.

4. A wish or urge from within; an impulse.

impulsion (ɪmˈpʌlʃən)

n

1. the act of impelling or the state of being impelled

2. motion produced by an impulse; propulsion

3. a driving force; compulsion

There seems to be different types of compulsions: 

compulsion: 

Irresistible Impulse - An urge to do or say something that might be better left undone or unsaid. 

Irrational Impulse: - A strong spontaneous and irrational motivation. 

Obsession: - An irrational motive for performing trivial or repetitive actions, even against your will.

Irrational Motive: - A motive inconsistent with reason or logic.

Onomatomania: - Obsession with a particular word which the person uses repeatedly or which intrudes into their consciousness.

So compulsions are impulses with a driving force behind them. 

It's interesting about that... Onomatomania... I haven't heard of that before. You know why it's interesting? For years I have wondered why I say this phrase spontaneously and often repeatedly.