from the GNU version of the Collaborative International Dictionary of English
- adj. Consisting of two threads twisted together; using two threads.
- adj. Having two screw threads instead of one; -- said of a screw in which the pitch is equal to twice the distance between the centers of adjacent threads.
from The Century Dictionary and Cyclopedia
- Having or sewing with two threads, as a sewing-machine having both needle and shuttle.
- Having two screw-threads which start at points 180 degrees apart and have each twice the pitch which appears from measuring from the tip of one thread to the tip of the next parallel to the axis. Double-threaded screws give very rapid motion to the nut.
Sorry, no etymologies found.