吸 + 一口气 / 深吸一口气
吸 (xī) means "to inhale," "to breathe in," or "to suck in" and describes the action of drawing air or a substance inward. A very common collocation is 深吸一口气 (to take a deep breath). It also appears in compounds like 吸引 (to attract) and 呼吸 (to breathe).
紧张的时候,深吸一口气会让人放松不少。
jǐnzhāng de shíhou, shēn xī yī kǒu qì huì ràng rén fàngsōng bù shǎo.
When you're nervous, taking a deep breath can help you relax a lot.
他站在山顶上,吸了一口新鲜空气。
tā zhàn zài shāndǐng shàng, xī le yī kǒu xīnxiān kōngqì.
He stood on the mountaintop and took a breath of fresh air.
医生让她慢慢地吸气,再慢慢呼出来。
yīshēng ràng tā mànmàn de xīqì, zài mànmàn hū chūlái.
The doctor told her to slowly breathe in, then slowly breathe out.