qí​yī

one of

其一 qí​yī
one of pronoun
one of the given options, items, or reasons

This is one of the reasons for the failure.

firstly pronoun
used to introduce the first point in a sequence or list

There are two reasons: first, time is tight; second, there is a lack of manpower.

Frequency

Movie subtitles
1.25 per million appears in 1% of films
Written text
11.2 per million

Sources

Definitions
CC-CEDICT