very boring or unexciting—‘(as) dull as ditchwater’ (1770)—the later phrase ‘(as) dull as dishwater’ (1832) is probably due to mispronunciation of ‘ditchwater’ in the original phrase
to describe or portray someone or something in very general terms, avoiding or neglecting the finer details—UK, 1808—alludes to a style of painting characterised by the use of broad brushstrokes
a Japanese figurine of a sitting cat beckoning with one raised paw, traditionally believed to bring good luck—USA, 1894—from Japanese ‘maneku’ (to invite by beckoning, especially with the hand) and ‘neko’ (a cat)
a perceived loss of intelligence or critical thinking skills—apparently coined after ‘potato rot’ by the U.S. author Henry David Thoreau in Walden; Or, Life in the Woods (1854)
UK, 1832—consolation taken from the fact that a bad situation is not worse than it is—one of several expressions in which the adjective ‘Dutch’ is used derogatorily or derisively
UK, 1963—with reference to the Beatles, a pop and rock group from Liverpool: the fact, or state, of being, or of resembling, a member of the Beatles; the world of the Beatles