Rune

From the Royal Irish Academy's Dictionary of the Irish Language:

Rún: a) something hidden or occult, a mystery or hidden meaning; b) a secret; c) secret thoughts or wishes, intention, purpose; d) full consciousness, knowledge; e) darling, love.

As I am fond of telling my students, the Celts were (in)famous for things starting with B — booze, bronze, bards and britches. These thoughts may or may not be related.