1.
armpit; underarm
The hollow area under the arm where it joins the body. Used in everyday, medical, and hygiene contexts.
脇の下で体温を測る。
To take one's temperature under the armpit.
脇の下に汗をかいた。
I sweated under my arms.
脇の下に体温計を挟んで五分待ってください。
Please place the thermometer under your arm and wait five minutes.
In Japan, the standard way to measure body temperature is under the armpit (脇の下で測る), unlike in some Western countries where oral thermometers are common. Common collocations: 脇の下に汗をかく (to sweat under the arms), 脇の下に挟む (to hold under the arm). Also written as 腋の下 with a different kanji. Sometimes shortened to simply 脇 in casual speech.