Expressions (phrases, clauses, etc.), Noun
1. two things that are superficially similar but completely different; night and day; chalk and cheese; the Moon and a turtleIdiomatic expression
Other forms
月とすっぽん 【つきとすっぽん】、月と鼈 【つきとすっぽん】
Notes
月と鼈: Rarely-used kanji form.