navel
臍 centers on the navel, the small scar on the abdomen where the umbilical cord was attached.
臍 combines the flesh radical ⺼ with 齊, which likely contributes the sound and may relate to the idea of a central point, like the navel at the body's center.
The flesh radical ⺼ beside 齊 suggests a part of the body that is central or even, like the navel in the middle of the belly.
For セイ, imagine saying 'say' while pointing to your navel: 'say' -> セイ, and the navel is the body's central point.
navel; belly button
umbilical cord
navel; belly button
bitter regret
fulcrum peg (fitted into the cavity in an oar as part of a traditional oarlock)
belly-button lint; navel fluff
to regret bitterly; to be very sorry (for); to bite one's navel
to make up one's mind (to do something); to resolve firmly (to do something)
navel piercing; belly button ring
navel piercing; belly button ring
umbilical hernia
lower abdomen
pit of the stomach
umbilical artery
circumference of the navel; treasure trail; sagittal hair
umbilical cord prolapse
umbilical artery
umbilical cord coiling
umbilical cord prolapse
umbilical cord blood