Bloom filter: That's assuming your vocabulary is reasonably finite. http://www.ling.helsinki.fi/~fkarlsso/genkau2.html has a list of forms for a single finnish noun. That's including case, possessives and clitics, but you can also have compounding (eg. several nouns in a row as one word) and derivations into other parts of speech (verbs become nouns etc). And once you've found out it's misspelt, you need suggestions..