A mason’s tool, used in spreading and dressing mortar, and breaking bricks to shape them.
A gardener’s tool, shaped like a scoop, used in taking up plants, stirring soil etc.
A tool used for smoothing a mold.
(transitive) To apply (a substance) with a trowel.
(transitive) To pass over with a trowel.
(colloquial, figurative) To apply something heavily or unsubtly.