1. [1950s+] (US black) to scrutinise, to uncover something that was meant to be kept secret by checking.
2. [1960s+] (also peep out) to put someone or something under surveillance; in weak use, to watch, to look at.
3. [1990s+] to pay close attention, to listen to what somebody is saying.
see under hole card n.
[1990s+] (US black) to see what is going on.