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

• IPA^(key): [a̠ma̠kɯ̟ᵝsa̠]

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): [tẽ̞ŋɡɯ̟ᵝsa̠]

天(てん)草(ぐさ) or 天草(テングサ) • (tengusa) 

1. any of the red algae of the genus Gelidium
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.

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

• Etymology at Nihonjiten (in Japanese)