Phonetic shift: /ariɡataku/ → /ariɡatau/ → /ariɡatoː/.
From ありがたく (arigataku), the adverbial form of Old Japanese and Classical Japanese adjective ありがたし (arigatashi, modern ありがたい arigatai, “grateful, thankful; welcome”), from 有り (ari, the 連用形 (ren'yōkei, continuative or stem form) of verb 有る aru, “to exist, to be”) + 難し (katashi, “hard, difficult”, 難い katai in modern Japanese). The katashi changes to gatashi as an instance of rendaku (連濁).
Modern Japanese -i adjectives formerly ended in -ki for the attributive form. This medial /k/ dropped out during the Muromachi period, both for the attributive form (-ki becoming -i) and for the adverbial form (-ku becoming -u). However, the adverbial form reverted back to -ku thereafter for most words, with the -u ending persisting in certain everyday set expressions, such as arigatō, ohayō, or omedetō, and in hyper-formal speech.
Arigatashi is first attested in the oldest literature of the 8th century. Originally meant “difficult to exist, hard to be”, shifting to “rare, special”, and then to “welcome, thankful, nice to have” by some time in the 15th century. This sense is still in use:
この天気はありがたいね。 ― Kono tenki wa arigatai ne. ― This weather sure is welcome.
- an expression of thankfulness: thank you
- Most often written in hiragana. May occasionally be seen spelled in kanji as 有り難う or 有難う, generally for more formal writing.
- The full form is ありがとうございます (arigatō gozaimasu). May also or alternatively be preceded by intensifier どうも (dōmo, “very”), 大変 (taihen, “very”) or 本当に (hontō ni, “really”). Expressions of thanks are given below in rough order of casual to polite.
- It can be preceded by くれて (“kurete”) to show the action to be thanked.
- どうも (dōmo)
- おおきに (ōkini) (chiefly Kansai)
- ありがとう (arigatō)
- どうもありがとう (dōmo arigatō)
- ありがとうございます (arigatō gozaimasu)
- どうもありがとうございます (dōmo arigatō gozaimasu)
- 1988, 国語大辞典（新装版） (Kokugo Dai Jiten, Revised Edition) (in Japanese), Tōkyō: Shogakukan
- 1995, 大辞泉 (Daijisen) (in Japanese), Tōkyō: Shogakukan, ↑ISBN
- 2006, 大辞林 (Daijirin), Third Edition (in Japanese), Tōkyō: Sanseidō, ↑ISBN
- ^ “Japanese Adjective Usage ― High Formality”
- ^ c. 759, Man'yōshū (book 17, poem 4011); online text at the University of Virginia