Awesome. Or perhaps I should say it with an American accent, because it became very fashionable amongst the valley girls in California in the 1980s, helped by its catch-use in that film, 'Bill and Ted's Excellent Adventure', along with a whole host of other cool words like, 'dude' and 'bogus'. Awesome! Yeah!
Well, originally, of course, the word was quite literal - inspiring awe, profound wonder. People would talk about 'an awesome sight' or 'the awesome power of the sun', but the American usage weakened the meaning and it became simply something beyond what is usual, something exceptional, something very impressive, it's great, it's cool, and that's the way in which the word has come to be used more than anything else these days. Anything can be 'awesome' now - 'that was an awesome car I just saw', 'that was an awesome cast on the show', or people just say, you know, 'it's awesome!' and it's not quite clear what that means, except that the person is simply affirming delight in something that's just happened.
It's a young person's usage. I have heard some older people use it - it's not a word I use myself, I have to say, and young people do, of course, make it even more intense - they put adverbs before it, 'that's totally awesome!', 'that's truly awesome!'. I even heard somebody say recently 'that's wicked awesome!'
Well, I think it's still around but, for many, it's dated now. I asked a couple of teenagers whether they'd use it and they said they 'wouldn't be seen dead using it these days; it's history', they said.