a. 1. Capable of being turned down; specif. (Elec.), Designating, or pertaining to, an incandescent lamp with a small additional filament which can be made incandescent when only a small amount of light is required. [ Webster 1913 Suppl. ]
2. Made to wear with the upper part turned down; as, a turndown collar. [ Webster 1913 Suppl. ]