sac
noun [ C ] uk/sæk/ us/sæk/
(BAG OF LIQUID)
biology specialized（动植物的）囊，液囊
a part of a plant or animal that is like a bag and often contains liquid
(SWOLLEN AREA)
medical specialized脓肿
a type of abscess (= swollen area containing a thick yellow liquid) under the skin
(TUMOUR)
medical specialized（肿瘤的）囊膜
a covering that surrounds a tumour