flatten

v. t. [ imp. & p. p. Flattened p. pr. & vb. n. Flattening. ] [ From Flat, a. ] 1. To reduce to an even surface or one approaching evenness; to make flat; to level; to make plane. [ 1913 Webster ]

2. To throw down; to bring to the ground; to prostrate; hence, to depress; to deject; to dispirit. [ 1913 Webster ]

3. To make vapid or insipid; to render stale. [ 1913 Webster ]

4. (Mus.) To lower the pitch of; to cause to sound less sharp; to let fall from the pitch. [ 1913 Webster ]

To flatten a sail (Naut.), to set it more nearly fore-and-aft of the vessel. --
Flattening oven, in glass making, a heated chamber in which split glass cylinders are flattened for window glass. [ 1913 Webster ]