armpit has definitions from the fields of anatomy,zoology
1
[ noun ] (anatomy,zoology) the hollow under the arm where it is joined to the shoulder

Examples

"they were up to their armpits in water"

Used in print

(Clayton C. Barbeau, The Ikon....)

The walk and his fears had served to overheat him and his sweaty armpits cooled at the touch of the night air .

*