Foreign words

I just lost a Facebook Scrabble game that I was ahead in, because my opponent laid down the bingo TZIGANE on his turn. Since I had no clue as to what it meant, I did some research, and turns out that it is a French word that means "gypsy" in English. I know some foreign words are playable because of the common usage in English concept, but I'm not sure why this word was allowed...to me it certainly doesn't fall into the same category as CIAO or ADIOS. Anyone have an answer??