Permanent

1. Continuing in the same state, or without any change that destroys form or character; remaining unaltered or unremoved; abiding; durable; fixed; stable; lasting; as, a permanent impression.
   
Permanent gases (Chem. & Physics),
hydrogen, oxygen, nitrogen, and carbon monoxide; -- also called incondensible gases or incoercible gases, before their liquefaction in 1877. The term is now archaic.
Permanent way ,
the roadbed and superstructure of a finished railway; -- so called in distinction from the contractor's temporary way.
Permanent white (Chem.),
barium sulphate (heavy spar), used as a white pigment or paint, in distinction from white lead, which tarnishes and darkens from the formation of the sulphide.