Do I really need a dictionary to tell me what "down" means? Dunno. Depends on whether you might have forgotten that as well as "in the direction of gravity" it

Do I really need a dictionary to tell me what "down" means? Dunno. Depends on whether you might have forgotten that as well as "in the direction of gravity" it also means "small soft feathers" and "small round hill", or that in the first of those senses it has an associated verb to describe knocking people down or consuming a drink quickly and a bunch of metaphorical uses (e.g., "away from Cambridge University" or "depressed"). Or whether you have any interest in knowing the etymology of any of these, or when they entered the language, or how they relate to one another. I use dictionaries about as often for looking up common words as for looking up obscure ones.