noun
a blow; a shock
Almost always used in the idiom 一泡吹かせる (ひとあわふかせる), meaning to give someone a shock or a scare, or to startle them. Rarely used independently.
彼の突然の辞任は会社に一泡吹かせた。
His sudden resignation gave the company a shock.
ライバルに一泡吹かせる作戦を考えて
We're thinking of a plan to give our rivals a scare.
泡 means 'bubble' or 'foam'. 一泡 is a bound form that appears almost exclusively in the idiom 一泡吹かせる, where it metaphorically means a shock or blow.
The exact derivation is uncertain. The kanji 一 (one) and 泡 (bubble) combine to form a metaphorical expression for a sudden shock, as if blowing a bubble at someone to startle them.