armpit arm·pit (ärm'pĭt')
n.
The hollow under the upper part of the arm below the shoulder joint, bounded by the pectoralis major, the latissimus dorsi, the anterior serratus muscles, and the humerus, and containing the axillary artery and vein, the infraclavicular part of the brachial plexus, lymph nodes and vessels, and areolar tissue. Also called axilla, axillary fossa.