Axilla
The axilla (also, armpit, underarm or oxter) is the area on the human body directly under the joint where the arm connects to the shoulder. It also provides the under-arm sweat gland.
In humans, the formation of body odor happens mostly in the axillary region. These odorant substances serve as pheromones which play a role related to mating. The underarm regions seem more important than the genital region for body odor which may be related to human bipedalism.
Wikipedia
Axilla (noun)
The armpit, or the cavity beneath the junction of the arm and shoulder.
Axilla (noun)
alternative form of axil
Axillae (noun)
plural of axilla
Wiktionary
Axilla (noun)
an armpit, or the corresponding part in a bird or other animal.
Axilla (noun)
an axil.
Oxford Dictionary