noun-modifying (irregular)
enlarged; swollen; fat
Prenominal form of 肥大する, used to describe something that has become enlarged, swollen, or excessively fat. Often medical or descriptive.
An enlarged liver was found during the health checkup.
I underwent surgery to remove the swollen tissue.
Compound of 肥 (hi, 'fat, fertile') and 大 (dai, 'big, large'), combined with the past/prenominal form of する. The kanji combination conveys the idea of becoming fat or enlarged.