一人ひとりきり

Meanings

Emphasizes being completely alone, with no one else present. Often used adverbially with で or as a noun with の. Similar to 一人っきり, but 一人きり is slightly more common.

Kanji

一one, one radical (no.1)
人person
独single, alone, spontaneously
切cut, cutoff, be sharp

Related words

一人ひとりっきり
Almost identical in meaning; 一人っきり has a geminated っ, which can sound slightly more emphatic or colloquial. Both are interchangeable in most contexts.
一人ひとり
Means 'one person' or 'alone', but without the strong emphasis on being completely alone that きり adds. 一人きり stresses the absence of others more strongly.

Written forms

一人ひとりきり
Standard kanji-kana spelling; 一人 is the usual way to write 'one person'.
独ひとりきり
Emphasizes solitude or aloneness; 独り carries a nuance of 'alone' rather than just 'one person'.
一人ひとり切きり
Less common kanji spelling using 切り; きり is more often written in kana.
独ひとり切きり
Rare combination of 独り and 切り; both kanji are uncommon in this word.
１ひと人りきり
Numeral spelling; sometimes used in informal writing or for brevity.
１ひと人り切きり
Numeral plus 切り; very rare.

Etymology

Compound of 一人 (ひとり, 'one person') and きり, a suffix meaning 'only' or 'just', derived from the verb 切る (きる, 'to cut'), implying a limit or boundary. The combination emphasizes being limited to just one person.