It's not uncommon for a search engine to take a word that is searched for, say "vase" or "obscure", and extrapolate the results to include common versions of the word. So using the earlier examples, you'd include "vases" for results of "vase" and conjugations like "obscures", "obscuring", or "obscured" for results of "obscure".
There's a term for this process, I learned it once and we mention it now-and-then as we talk about our own search system (guess what I'm about to report a bug in! ♪), but I've forgotten the term and cannot find it again. Do you know what the term for this is? Is this in fact a common and accepted term?