not entirely unlike X

Used ironically of things which are in fact almost entirely unlike X, except for one feature which the speaker clearly regards as insignificant. "That is not entirely unlike cool...at least it's small". Comes directly from the Hitchiker's Guide to the Galaxy scene in which the food synthesizer on the starship Heart of Gold dispenses something "almost, but not entirely unlike, tea".

--The Jargon File version 4.3.1, ed. ESR, autonoded by rescdsk.