latch onphrasal verb
British English informal
He's so thick it took him ages to latch on.
latch onto somebody/somethingphrasal verb
to become very interested in something:
Don't just latch on to the latest management fads.
to follow someone and keep trying to talk to them, get their attention etc, especially when they would prefer to be left alone:
He latched onto Sandy at the party and wouldn't go away.
to hold tightly to something with your hand, mouth etc:
a baby latching on to its mother's breast