boil and abscess

今日も昨日と同じく "Amazing Medical Mysteries... Solved" の記事から別の病気の話です。
A man in his 20s came into the emergency room with a painful boil in his left armpit that had been getting larger for about three weeks. The abscess didn't have the usual redness, plus it had been growing for much longer than a typical abscess.
上記にある "boil" と "abscess" の意味は知りませんでしたが（もちろん "boil" は知ってはいますが、ここでの意味ではありません） 、どちらも「腫れ」の意味だろうと推測できます。辞書で確認します。まず "boil" の項を見ます。
・Collins Dictionary: a red painful swelling with a hard pus-filled core caused by bacterial infection of the skin and subcutaneous tissues, esp at a hair follicle Technical name: furuncle
・Macmillan Dictionary: a painful lump on your skin that has become infected and is filled with pus (=an unpleasant yellow liquid)
次に "abscess" を見ます。
・Collins Dictionary: a localized collection of pus formed as the product of inflammation and usually caused by bacteria
・Macmillan Dictionary: a painful swollen area on your skin or inside your body that is infected and filled with pus (=unpleasant yellow liquid)
単なる「腫れ」ではなく、膿もある腫れですね。