Dictionary.net

Make s. (often out, over, down, away; s. over or a way differences, perplexities, difficulties, &c., reduce or get rid of in fact or appearance); free from impediments or discomfort (s. the way; will his declining years); cloak over faults &c.; become s. (usu. down; sea presently smoothed down); smoothing-iron, implement usu. heated to s. linen &c.; smoothing-plane, small plane for finishing the planing of wood.

(gave his hair a s.).