The best replacement for viscosity is density.

The best alternatives to viscosity are rated as following:
★★★★★  density
★★★★★  shear rate
★★★★★  temperature
★  flow rate
★  specific gravity
★  tunnelblick
★  surface tension
★  molecular weight
★  high viscosity
★  pressure drop
★  low viscosity
★  flow
★  consistency
★  temp
★  openvpn
  intermolecular forces
  viscosity index
  kinematic viscosity
  shear stress
  temperature water
  dynamic viscosity
  temperature of water
  temperature for oil
  particle size
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Your alternative for viscosity is not listed? Suggest!
Speaking about viscosity, one probably shouldn't forget about intermolecular forces.

Other search terms related to viscosity and their ratings are:
★★★★★ intermolecular forces
★★★★★ volcanoes
★★★ liquids
★★ molecular weight
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viscosity
density
shear rate