That word was written down wrong. It sounds like mátturinn to me.

A few other bits are also written incorrectly. For instance this "óð það snjó" I believe is actually "óð þar snjó" (otherwise the cases don't make sense), so that bit would be "one woman waded there through the snow in a black blizzard with the devil in a bottle". It's easier to understand if you move the components around like this: Ein óð þar snjó í svörtum byl með vítið í flöskunni. Seems to be a song about a woman who gets drunk and dies of exposure.

And of course it should be tómarúm not tömarúm, but you got that one ;)

Sátt there is the adjective sáttur, not the noun sátt (again, you can tell from the cases).

Hope you don't mind, saw you were asking for help on this one.