(idiomatic) One's innermost private feelings.

(obsolete, inorganic chemistry) potassium bromide

(obsolete, chemistry) potassium plumbate

(obsolete, inorganic chemistry) potassium carbonate

(obsolete, inorganic chemistry) potassium chromate

Previously unknown; unprecedented. / Unknown or known to only few people.

A feudal title of the hereditary proprietor of a manor in manorialism; now largely ceremonial.

(physics) The theories of special relativity and general relativity, two theories in physics developed mainly by Albert Einstein at the beginning of the 20th century from which several important results such as the equivalence of matter and energy and the Einstein field equations are derived.

(idiomatic) To be particularly, especially uncannily, observant; a perceived ability to see in all directions at once.

(UK, Australia) Cease to boil when heat is no longer applied. / (idiomatic, UK, Australia) To lose interest; to pall. / (idiomatic, UK, Australia) To become of diminished intensity or urgency.