Why didn't Morgoth act when he had the chance?

[The Saucepan Man]

I just don't like people calling Melkor 'Morgoth' before his 'full' transformation, after the chaining of the Valar. Melkor was a character of far more potency, read 'Myths Transformed' for more details.

Well, I've only read the Silmarillion (and only the first few chapters at that, so far), and that gives the impression that Morgoth was simply the name given by Feanor to Melkor after he destroyed the Two Trees and slayed Finwe:

Then Feanor rose, and lifting up his hand before Manwe he cursed Melkor, naming him Morgoth, the Black Foe of the World; and by that name only was he known to the Eldar ever after.

So, I kind of use the two names interchangably.