SWELLING. When the word is used in the context of the human body, it refers to an increase in size of an affected part. It often is due to inflammation in the part caused by noxious substances present in the tissue spaces such as: (1) blood clot resulting from injury, (2) infection with bacteria, (3) insect sting, or (4) snake venom such as pit viper venom (see Poison) which dissolves red blood cells and causes retention of fluid in the affected part. Blocked lymph vessels or blood vessels (e.g. blood clot in a vein) may also cause swelling. Likewise tumors, such as cancer, cause swelling by the nature of their growth. (See Lev 13:2; Num 5:21; Acts 28:5.)
International Standard Bible Encyclopedia (1915)
In the 2Co 12:20 for phusiosis, "puffing up," "blatant self-conceit," and 2Pe 2:18 parallel Jude verse 16 for huperogkos, "overgrown," "solemnly inane."