1. A solid material's ability to deform under tensile stress (pulling).
2. The quality of being flexible or malleable.
Today's word is brought to you by the lyrics for "Lonely Lab of Broken Hearts" by The Arrogant Worms.
If you've seen the "backwards bicycle" video, it seems a good example of the relative ductility of a child's mind compared to an adult's.
Etymology: from Latin ducere, to lead.