From Longman Dictionary of Contemporary Englisharmpitarm‧pit /ˈɑːmˌpɪt $ ˈɑːrm-/ noun [countable] 1 HBHthe hollow place under your arm where it joins your body2 → the armpit of something
Examples from the Corpus
armpit• But in a moment or two he released Glover and shoved his two hands inside his armpits.• The General tucked the baton under his armpit and clapped his hands softly as the small orchestra walked through his study.• They also disagree about whether the glands in the armpit should be removed, treated with radiotherapy, or left alone.• He suddenly seized her under the armpits and swung her round and round, until she was breathless. 