Many Japanese words of Portuguese origin entered the Japanese language when Portuguese Jesuit priests and traders introduced Christian ideas, Western science, technology and new products to the Japanese during the Muromachi period (15th and 16th centuries).

The Portuguese were the first Europeans to reach Japan and the first to establish direct trade between Japan and Europe, in 1543. During the 16th and 17th century, Portuguese Jesuits had undertaken a great work of Catechism, that ended only with religious persecution in the early Edo period (Tokugawa Shogunate).

Many of the words which were introduced and entered the Japanese language from Portuguese and Dutch are written in kanji or hiragana, rather than katakana, which is the more common way to write loanwords in Japanese in modern times. Kanji versions of the words are ateji, characters that are "fitted" or "applied" to the words by the Japanese, based on either the pronunciation or the meaning of the word.

The † indicates the word is archaic and no longer in use.

Some word pairs that appear similar are actually false cognates of unrelated origins.

Arigatō

Look up ありがとう in Wiktionary, the free dictionary.

It is often suggested that the Japanese word arigatō derives from the Portuguese obrigado, both of which mean "Thank you", but evidence indicates arigatō has a purely Japanese origin,^[20] so these two words are false cognates.

Arigatō is an "u"-sound change of arigataku.^[21] In turn, arigataku is the adverbial form of an adjective arigatai, from older arigatashi,^[22] itself a compound of ari + katashi. Written records of arigatashi exist dating back to the Man'yōshū compiled in the 8th century AD,^[22]: (1) well before Japanese contact with the Portuguese in the 16th century.

Ari is a conjugation of verb aru meaning "to be", and katashi is an adjective meaning "difficult", so arigatashi literally means "difficult to exist",^[22] hence "rare" and thus "precious",^[22]: (3) with usage shifting to indicate gratitude for receiving an outstanding kindness.^[22]: (5) The phrase to express such gratitude is arigatō gozaimasu,^{[21]: (イ)} or arigatō for short.^{[21]: (ロ)}

• Gairaigo
  • List of gairaigo and wasei-eigo terms
• Japanese words of Dutch origin
• Nippo Jisho, the first Japanese dictionary in a Western language