To toil, to work.
To belabour, to emphasise or expand upon (a point in a debate, etc).
I think we've all got the idea. There's no need to labour the point.
To be oppressed with difficulties or disease; to do one's work under conditions which make it especially hard or wearisome; to move slowly, as against opposition, or under a burden.
To suffer the pangs of childbirth.
To pitch or roll heavily, as a ship in a turbulent sea.
Expressive of strenuous effort.
At the end of the marathon, her laboured breathing told us she was exhausted.
Of writing or speech or similar, stilted or not natural due to too much effort being used in the production.