(adjective) being less dense / (adjective) of, relating to, or interesting to a select group; esoteric / (adjective) very high / (verb) to make rare, thin, porous, or less dense; to expand without the addition of matter / (verb) to make more spiritual, refined, or abstruse / (verb) to become less dense
Nabokov’s sentences go on for lines and sometimes pages, and his highfalutin diction sprouts naturally from his polyglot education and rarefied background