Synonyms for Thickness:

n.

length, depth, spread, span, gauge, girth. thick. as a measurement (noun)
depth, breadth.
as a quality (noun)
closeness, heaviness, solidity, concentration.
attribute (noun)
heaviness.
dark (noun)
denseness.
denseness (noun)
girth, compactness, width, layer, density, diameter.
density (noun)
cohesion, denseness, solidity, compactness.
gauge (noun)
gauge.
heaviness (noun)
heaviness.
thickness (noun)
bulk, caliber, expanse, width, density, breadth, heaviness, diameter.
width (noun)
girth.

Other synonyms:

girth. length. span, gauge. depth. spread. stratum
layer.
Other relevant words:
concentration, condensation, closeness, heaviness, cover, membrane, layer, blanket, length, skin, span, plate, frailty, thick, spread, gauge, girth, paint, depth, surface.

Usage examples for thickness

  1. In front of it, on the roof, seen against a white house opposite, stood a demon of a cat, arched to half its length, with a tail expanded to double its natural thickness – David Elginbrod by George MacDonald
  2. Setting out he pierced, followed by his men, through the thickness of the forest, and advanced to meet the Franks. – A Popular History of France From The Earliest Times Volume I. of VI. by Francois Pierre Guillaume Guizot