天草

Orthographic borrowing from Japanese 天草 (Amakusa).

天草

1. (～市) Amakusa (a city in Kumamoto Prefecture, Japan)

Compound of 天 (ama, “heavens”) +‎ 草 (kusa, “grass, plant”).

The surname likely comes from the place name, the derivation of which is uncertain. Theories include:

• Named for the 海人 (ama, “sea people”) 草 (kusa, “tribe”) that lived in the archipelago in the region, as reported in the Nihon Shoki (720 CE)
• Named for the 甘草 (kanzō, “licorice”, literally “sweet grass”, alternative reading amakusa) harvested in the area
• Shift from 馬草 (makusa, umakusa, literally “horse grass”) from grazing areas in the region

• (Tokyo) あまくさ [àmáꜜkùsà] (Nakadaka – [2])
• IPA^(key): [a̠ma̠kɯ̟sa̠]

天(あま)草(くさ) • (Amakusa) 

1. Amakusa (a city in Kumamoto Prefecture, Japan)
2. a rare surname

Compound of 天 (ten, “heavens”) +‎ 草 (kusa, “grass, plant”). The kusa changes to gusa as an instance of rendaku (連濁).

Uses the on'yomi of ten for the 天 character.

• (Tokyo) てんぐさ [tèńgúsá] (Heiban – [0])^[1]
• IPA^(key): [tẽ̞ŋɡɯ̟sa̠]

天(てん)草(ぐさ) or 天草(テングサ) • (tengusa) 

1. any of the red algae of the genus Gelidium

   Synonym: 心太 (tokoroten)

2. agar

As with many terms that name organisms, this term is often spelled in katakana, especially in biological contexts (where katakana is customary), as テングサ (tengusa).

• 寒天(かんてん) (kanten)
• 心太(ところてん) (tokoroten)

• Etymology at Nihonjiten (in Japanese)