Armpit
Under One's Arm
noun
The kanji and the word are exactly the same. That means they share meanings as well.
わき
The reading is the same as the one you learned with the kanji. Now isn't that a bit wacky (わき)?
俺が逆らうと、兄貴はよく脇をこしょばしてきました。
My older brother used to tickle my armpits when I opposed him.