Also found in: Dictionary, Thesaurus.
Related to know from: know from Adam
know (someone or something) from (someone or something else)
To be able to distinguish a particular person or thing from someone or something else. Usually used in negative constructions. I've heard his name before, but I wouldn't know him from a stranger on the street. My father is so hopeless when it comes to technology that I'm surprised he knows a mouse from a monitor.
not know from (something)
To not know anything about something. From Yiddish, heard primarily on the East Coast of the US. Why don't you just stay out of this, OK? You don't know from running your own business. Ah, don't mind her, Phil. She doesn't know from nothing.
know someone from someone
to tell the difference between one person and another. I don't knowFred from his twin brother. I know Bill from Bob, but I can't tell most identical twins apart.
know something from something
to tell the difference between one thing and another. (Often with a negative.) You don't know a smoked herring from a squid! She didn't know a raven from a crow, and who does?
know from something
to know about something. (Used on the eastern seaboard.) Do you know from thermostats? You don't know from anything!