The Portuguese etymology is not complete. How did the word evolve from the Latin meaning "obliged, made liable, having been bound by obligation." to its current usage to mean "thank you"? When was it first used as "thank you"?
The latter question could settle the controversy over whether there is any relationship between this word and Japanese "arigatō". The Japanese word seems to have been in use before Portuguese traders arrived (see  and arigatō), but was the word used as "thank you" by the Portuguese prior to 1542? - 18.104.22.168 16:10, 17 February 2013 (UTC)