nativity, be born, declension, lie, be arbitrary
誕 centers on coming into existence or being brought forth: being born or nativity. The senses of lying or being arbitrary are extensions of making something up or fabricating a story out of nothing.
誕 combines 言 (speech) with 延, which likely contributes the sound and the idea of extending or stretching. The core meaning of birth may come from the idea of extending a family line, while the lying sense relates to stretching the truth with words.
Words 言 that stretch 延 the truth can give birth to lies. Picture a tall tale being born from someone's mouth.
For タン, imagine a tanuki giving birth to a litter of little tanuki while telling tall tales: tan -> タン.
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birth (of a person); nativity
birth (esp. of a famous person); nativity
sudden emergence; sudden formation; coming out of nowhere; bursting onto the scene
birthstone
Emperor's Birthday (national holiday; February 23)
birth (of a saint, monarch, etc.); nativity
Christmas
birthday party
birthday
happy birthday!
happy birthday
(seat at) the head of the table; seat of honour (honor)
Nativity group; Christmas crib
Christmas
Victoria Day (Canadian public holiday)
rebirth; reincarnation
virgin birth (esp. of Jesus)
first birthday
The Birth of Momotaro (book by Yanagita Kunio)
100th birthday anniversary