anus
肛 refers specifically to the anus, the external opening of the rectum.
肛 combines the flesh radical ⺼ (body part) with 工, which likely provides the sound. The character was created to represent the anatomical anus.
The flesh radical ⺼ indicates a body part, and 工 looks like a simple opening or passage. Together they point to the body's rear opening: the anus.
For コウ, imagine a doctor saying 'Cough!' during an examination, and the patient tenses up: cough -> コウ, while the focus is on the anus.
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anus
anal prolapse
artificial anus
entoproct (any animal of phylum Entoprocta)
ectoprocta; bryozoa; moss animals
post-anal tail
postanal gut; post-anal gut; postcloacal gut
anal epithelium
anal bleeding; bleeding of the anus
proctology
anal valve; valvulae anales
anal sex; anal intercourse
anal character (in psychoanalysis)
anal sphincter
levator anus muscles; levator ani
anal stage
anorectal
proctology department; proctology clinic; proctology
anal gland
anoscope; proctoscope; rectal speculum