I found these from the instrumental case and they are in brackets such as : Армией (-ею)
If a feminine noun in the Instrumental case singular ends in "-ой", "-ёй" or "-ей" then it also has an alternative form (also the Instrumental case singular, of course) ending in "-ою", "-ёю" or "-ею" respectively. This is a regular stuff, so not all dictionaries even mention it.
However, in the modern language the forms ending in "-ою"/"-ёю"/"-ею" are rarely used except poetry and such.
Also feminine nouns ending (in the Nominative case) in the non-stressed "-ия", such as mentioned above "армия", are almost never put into this "alternative form", because of a discordance.
While @Matt is right and those forms became obsolete at the end of XIX century, however, there are some forms that you still can encounter it in casual usage. It's very rare, it wouldn't be oversimplification to say - always stick to new endings (
-ью instead of
-ию), still, don't be surprised if you'll heard:
- Ты с головою, что ли, не дружишь совсем? (instead of c
- Ты куда ты с непокрытой головою на мороз?
- Ты рукою себе помог!
- C дядею пока посиди, мы через час будем.
It's difficult to google this though because, apart from this being rare , in media this just won't be acceptable and in written language native speaker would just use the correct form.
Also, once again, not to contradict Matt - this is only about very small set of short popular words, like
река etc. With
армией you'll never hear