What is something that holds wood together well?

i have this like 2 1/2 foot tall, 1 foot wide picture clock thing. its a picture, but theres a clock on it too. and its like 1/3 of an inch thick. its made of wood. like plywood, and some plastic..not exactly sure. and it probably weighs like a pound or so. its split right in half. what do you suggest i use to make it stick together cause when i hang it up, i dont want the bottom half to fall off