noun
Basic counting sense: a single human being. Often used with counters or in contexts specifying numbers of people.
会議には一人だけ来なかった。
Only one person didn't come to the meeting.
一人ずつ名前を呼ばれた。
Our names were called one by one.
noun
Only with reading ひとり
State of being alone, without others. Often used in phrases like 一人で (alone, by oneself) or 一人になる (to be alone).
See also: 一人で
彼は一人で暮らしている。
He lives alone.
たまには一人になりたい。
Sometimes I want to be alone.
noun
Only with reading ひとり
Specifically refers to being unmarried or without a partner. Often used with 独り.
彼はまだ独り身だ。
He is still single.
独りでいるのも悪くない。
Being single isn't so bad either.
adverb
Only with reading ひとり
Adverbial use: doing something alone, without help or company. Often 一人で.
この仕事は一人でできます。
I can do this work by myself.
彼女は一人で旅行するのが好きだ。
She likes traveling alone.
adverb
Only with reading ひとり
Used with a negative sentence to mean 'not just/only/simply'. Usually written in kana. Emphasizes that something is not limited to a single aspect.
この問題はひとり日本だけの問題ではない。
This problem is not just Japan's problem.
彼の失敗はひとり彼だけの責任ではない。
His failure is not solely his responsibility.