noun, noun which may take the genitive case particle 'no'
one star (rating)
Used for a single-star rating in reviews, evaluations, or rankings.
このレストランの評価は一つ星だった。
This restaurant had a one-star rating.
noun
Only when written 一つ星
Refers to a single bright star visible at dawn or dusk; often poetic or literary. Restricted to the 一つ星 spelling.
東の空に一つ星が輝いていた。
A single star was shining in the eastern sky.
Compound of 一つ (ひとつ, 'one') and 星 (ほし, 'star'), with rendaku voicing of ほし to ぼし.