From the Department of Words Found at Work Department:
Pyrophoric: Materials relating to and with propensity for spontaneous ignition in air; literarly “Fire Bearing” 
from the greek comb. form meaning “fire,” from Gk. pyro-, combining form of pyr (gen. pyros) “fire”; with phoric; euphoria + pherein “to carry”.
See MSDS Glossary:
A pyrophoric material can spontaneously ignite in air. Many pyrophoric materials are also water reactive, reacting vigorously with water or high humidity, often igniting upon contact.
See The Prodigy. Materials waiting. Waiting. Suddenly. Suddenly. Waiting. Without Warning. Combustion. Combustion. Combustion. Explode. What happens when a Firestarter goes inert?
science.