armpit
n. A2 Elementary US //ˈɑɹmˌpɪt// UK //ˈɑːmpɪt// armpit
n. the area under your arm where your arm connects to your body. It is a common word for this part of your body.
n. the area of the body under the arm where the arm joins the torso.
He wiped the sweat from his armpit.
The athlete wore a special sleeve to keep his armpit dry during the long race.
The surgeon carefully examined the armpit for signs of lymph node swelling before proceeding with the biopsy.
From Middle English armpitt, arme-pitt, armput, equivalent to arm + pit. (something unpleasant): Presumably a reference to underarm body odor.