"In grammar, inflection or inflexion is the modification of a word to express different grammatical categories such as tense, mood, voice, aspect, person, number, gender and case. Conjugation is the inflection of verbs; declension is the inflection of nouns, adjectives and pronouns. The Slavic languages, including Russian, Polish, Macedonian, Czech, Slovak, Serbian, Croatian, Bosnian, Ukrainian, Bulgarian, and Slovene among others, all make use of a high degree of inflection, typically having six or seven cases and three genders," explains Wikipedia.
Gmail is one of the Google services with a rudimentary search feature. Unlike Google Search or Google Docs, Gmail doesn't show spelling suggestions and it doesn't search for other forms of your keywords. If you search for "author", Gmail doesn't show messages that include the word "authors"; if you search for "web site", you won't find messages that only include "website".
I tried to add "morph:on" in Gmail's English interface, but it didn't work. Hopefully, Gmail will improve the search algorithms and the operator will be included by default for all languages.
{ Thanks, Jiri. }