盾 dùn shield

How it came to be

A shield seen from the front, an eye looking out over the top. The eye makes it a shield, not a board: somebody is behind it, watching.

Noun for "shield", almost always met in the compound 矛盾 (máodùn) "contradiction/conflict" - literally "spear and shield", from the classic idiom about a merchant who claimed his spear could pierce any shield and his shield could block any spear.
后盾 (hòudùn) "backing/support" extends the shield sense metaphorically: 坚强的后盾 "a strong backer".
Also used to write foreign currency names ending in "guilder/gulden", e.g. 印尼盾 (Yìnní dùn) "Indonesian rupiah" - an unrelated borrowed use worth noting so you're not confused by it in finance news.