One thing cannot live on its own yet, so a cord runs to it and carries what it needs: food, air, power, money, care. The cord feeds and holds at the same time. Sooner or later somebody cuts it, and after that the far end is on its own.
The compound is umbilical (of the navel) plus cord. It is first recorded in 1753 and gradually replaced the older English name navel-string.
這個詞由 umbilical（肚臍的）加 cord（繩、索）組成，字面就是「肚臍那條索」。最早的紀錄在 1753 年，後來慢慢取代了更早的說法 navel-string。
Wiktionary (kaikki extract, source_ref kaikki:3f6f69a190036ae4:865894931:35729): 'From umbilical + cord. Largely displaced native navel-string. First attested in 1753.'
Three branches
身體裡真的那條臍帶
這一支是字面用法，也是其他用法的來源。後面兩支都是把這個畫面搬到別的地方。
noun · B2
The soft tube that joins a baby to its mother while the baby is growing inside her. Food and air pass along it to the baby, and waste passes back out. It is cut soon after the baby is born.
臍帶
還沒斷開的補給線（太空、工程）
工程師把同一個畫面搬到機器上：東西還接在來源上，靠它供應，真正出發之前才鬆開。
noun · C1
In spaceflight, a line that carries air, power, fuel, or messages to something that is not yet on its own: from a spacecraft to an astronaut working outside it, or from the launch pad to a rocket before it lifts off.
維生管線（太空用）
人與人、人與地方之間的牽連
把「被餵養、也被綁住」的感覺搬到關係上：一邊靠著另一邊，而且不容易斷。
noun · C1
A very strong connection that ties a person, a group, or a piece of work to a place, a family, or where it came from, especially one that gives support and that someone may have to break before they can stand on their own.
臍帶般的牽連