Does anybody know?

Yeah. It can mean 'i got you' in a literal and physical way, like when chasing someone n catching them it's like 'gotcha!'
Or it can mean 'i get what you mean' / 'i know what you're talking about.' So since you understand what we're trying to say, you can say 'gotcha!'

HAHA. Wow. You must live some secluded life to attempt to look up colloquials in the dictionary. I couldn't find 'ouch' in the dictionary :(