What does "nombril" mean?

A point halfway between the fess point (centre of the shield) and the middle base (bottom) point of an escutcheon.

What is a synonym for "nombril"?

Common synonyms include: belly button, center, core, focus, foreign term, hub.

/ˈnɑmbɹəl/ noun

noun ·Rare ·Advanced level

Noun

1
A point halfway between the fess point (centre of the shield) and the middle base (bottom) point of an escutcheon.
2
the center point on a shield wordnet

Borrowed from Middle French nombril.