Суффикс -ою в творительном падеже

[Ignacio]

Здравствуйте.
I was translating some songs and came across with this two words:
'С фашистской силой тёмною' (от Священная война).
'Над планетою солнце встаёт' (от Гимн Путину).

I would want to know which is the nominative case of those two words and why the suffix -ою is used here. Also, I would want to know whether the expression 'в основанье' is properly written or it should be 'в основании'.

Заранее спасибо.

[RP01]

Hi,

The only "-ою" suffix rule I found is applied to form the instrumental case of feminine nouns by replacing the ending "a". In this case the good question is what was the original form it was cretaed?

The other thing I found is that the instrumental feminine form of adjective "тёмный" is "тёмною" but nowhere to find a russian adjective conjugation rule which would result in this.

so at this point:
1. There is a rule for "-ою" suffix which is for nouns and seems to be not applicable here.
2. The usage of the "-ою" suffix officially assigned to form a specific adjective case but the question is based on what rule?

I would join the original questioner to ask someone for explanation as it seems to be very interesting

Br
RP

[Olegas]

тёмною=темной
планетою=планетой
"ою" more expressive "ой"
"ою" is used at songs, poems, not ordinary conversation
"ой" for ordinary conversation
'в основанье' there's no such word , "в основании" , "в основе"
sorry for my bad english