particle, numeral, verb, place name · a quantifier indicating a single unit or entity

桌上有一个苹果。

numeral · numeral 'one' combined with classifier 'ge'

我想要一个苹果。

verb, numeral · indefinite article indicating a single entity or object

这架无人机内置了一个高精度的陀螺。

verb, numeral · a single instance of something, often used as a determiner meaning 'one'

他想要买一个苹果。

numeral, pronoun · an indefinite article or the numeral one

我有一个好主意。

numeral · the entire duration of a period of time, such as an afternoon or summer

他在那儿坐了一个下午。