Flat″ten (flăt″t'n), 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.
2. To throw down; to bring to the ground; to prostrate; hence, to depress; to deject; to dispirit.
3. To make vapid or insipid; to render stale.
4. (Mus.) To lower the pitch of; to cause to sound less sharp; to let fall from the pitch.
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.