I know two words: two for "language": "mowa" and "język" and one for tongue (an organ of the digestive system + organ of speech+ language): "język".
Someone already mentioned that another word for "tongue," the organ, is "ozór."
I agree that unusual grammatical patterns and non-Slavic vocabulary do play a part in the problems other Slavic speakers may have understanding Russian. Polish has considerable East Slavic influence, so those differences aren't as significant as for other Slavic speakers. For example, using "u mienia jest'" to indicate possession is odd, but not completely alien to Polish. "Czy tylko u mnie jest problem?" vs "Czy tylko ja mam problem?"
I think accent plays a much bigger role. I'd imagine most Polish speakers would agree, for example, that Slovak is much easier to understand than Czech, even though on paper, the written languages are almost identical and almost completely mutually intelligible. The main difference between Czech and Slovak is that Slovak tends to palatise consonants more, shorten some long vowels and in certain dialects, stress falls on the penultimate syllable as opposed to the first.
In Russian, I think it's both, the unpredictable, dynamic stress and the akanie (the reduction of unstressed vowels to 'a' or schwa) that make it difficult to recognise word boundaries, and make otherwise familiar words sound very different to Polish speakers. Ukrainian doesn't have akanie, which makes Ukrainian sound a lot less Russian and more familiar as far as vowels are concerned. Russian has more palatisation than Ukrainian, however, which makes Russian consonants sound more familiar. So the relative importance of vowels, consonants, accent, grammar and vocabulary to a person's individual understanding will mean people's opinions will vary as to which is easier to understand.