What does a knot under your arm mean?

KNOT UNDER ARM: A knot uder the arm -- the armpit -- can be a cyst, an infected cyst, a gland, and more, a node and more. See your doctor, particularly if it's sore or tender. Could be more than a "knot".

See below: Agree with Dr. L. If the "knot" is not bothering you, you may watch and wait. It is likely to be an enlarged lymph node. You may feel the node every couple of weeks, if the lymph gland doubles in size, becomes painful, ulcerates, or other nodes become enlarged, or you develop fever, or lose weight, you should see a doctor.