To widen or expand something. A noun can be used between "broaden" and "out" or after "out." They want to knock down a wall and broaden their kitchen out. I'm doing these exercises to broaden out my shoulders.
broaden something out
to make something wider; to expand something. Now, broaden this part out a little, so it looks like a cloud, not a painted pillow. Broaden out the river in your painting so it looks very wide. The photographic view of the valley can be broadened out by using a different lens.
to become wider; to expand. The river broadened out and became deeper. The road broadens out here.