息

In a sentence

• 私は深く息を吸いました。

  I took a deep breath.

  Here, '息' (iki) is used to mean 'breath' in the context of respiration.

• 彼の息づかいが速くなってきました。

  His breathing became faster.

  '息づかい' combines '息' (breath) with 'づかい' (usage) to refer to someone's way of breathing.

• この部屋に入ると息が詰まる気がする。

  It feels suffocating when entering this room.

  Here, '息' is associated with the act of breathing, and '息が詰まる' is a phrase expressing feeling suffocated or stifled.