Introduces the first of two (or occasionally more) options or possibilities, the second (or last) of which is introduced by “or”.

(linear algebra) A scalar, 𝜆, such that there exists a non-zero vector x (a corresponding eigenvector) for which the image of x under a given linear operator A is equal to the image of x under multiplication by 𝜆; i.e. Ax=𝜆x.

The cardinal number immediately following seventy-seven and preceding seventy-nine.

A gramophone record designed to be rotated at 78 revolutions per minute; a 78

Any of the species of the genera Polysticta or Somateria, in the seaduck subfamily Merginae, which line their nests with fine down (taken from their own bodies).

(Cockney rhyming slang) A state (of upset, worry).

(music) A blues form built on an eight-measure chord pattern, most typically I, I, IV, I, V7, IV, I, V7, where I, IV and V7 represent the tonic, subdominant and dominant seventh chords respectively.

Any of several annual festivals in which Welsh poets, dancers, and musicians compete for recognition.

Albert Einstein, the world-famous 20th-century theoretical physicist who developed the theory of relativity. / A surname from German.

(sometimes sarcastic) An extremely clever or intelligent person.