Hooking is usually what happens in a race course when you 'hook a gate'.
'Catching an edge' is when you are sliding your skis in a direction with some lateral component of movement (not 'perfect' carving) and the edge that is 'leading' catches the snow and stops the lateral movement. An example: you are making a right footed, brushed turn and your left ski's big toe edge grabs the snow.
I was going to reply with what first pooped into my head, but having read this post, I have to agree.
The general uneducated meaning I learned from context, the same way I learned to talk in general follows. Catching an edge: happens if one gets of balance and slightly out of perfect control. An edge gets put wrong and catches strongly in the snow, taking the ski where you don't want it to go. Example of catching an edge: you are turning left with a tipped, pressured and decambered right ski; the big toe edge of your left, unpressured ski catches the snow, pulls hard left and you fall on your face. Hooking: you tip your skis and they turn like they are supposed to, but you learned to ski in a gliding wedge, usually ski with low edge angles, and prefer to smear and pivot your turns and are taken off guard. Also hooking: you intend to turn left and tip your skis accordingly, but your skis hit a one-foot deep frozen solid rut and follow it. Lucky for you, nobody else is skiing in those conditions, so you can go where your skis are pointing without hitting anyone.