I had a lunch meeting with someone that turned out be "fortuitous" for someone else in my organization. In looking up that word as I wrote about our "fortuitous" meeting, I found that it really means "happening by accident or chance". According to AHD, perhaps because it sounds similar to "fortunate" or "felicity", it has evolved to mean "happy accident". However, the use of it to mean "fortunate" or "lucky" is more controversial, according to AHD, and indeed this use was labeled a "malapropism" in the 20s by Fowler.
My intended use was probably wrong, therefore, since the lunch had been planned and wasn't an accident.
Since "tu" is the Latin root from which several languages derive the second person pronoun, "for" and "tu" combined with "itous" must be an accident that is good "for you!"
