lay in transitive verb 1.: to store up : lay by < lay in an ample supply of groceries > 2.archaic: to assert as a claim 3. a.: to paint in roughly subject to finishing, elaboration, or addition b.: to put (masses of color) on a canvas < helped him to lay the background blues and browns in > 4. a.: to heel in (a plant) b.: train IV 2 5.Britain: to shut down or discontinue working (a colliery or coal pit)