thickening

Etymology

thicken + -ing

noun

1. The process of making something, or becoming, thick or viscous.
2. A substance, usually a source of starch, used to thicken a sauce.
3. A thickened part of a structure.
   They disappear at once on slightly relaxing the air-pressure, whilst true incipient thickenings of the surface remain white and unpliably stiff. 1902, Edwin Hurry Fenwick, Obscure Diseases of the Urethra, page 30

verb

1. present participle and gerund of thicken

adj

1. Beginning to thicken, becoming thicker.
   From Keighley onwards we had obviously returned to civilisation, for the surrounding country was now studded with the sodium street lights of suburbia and a thickening industrial haze was blotting out the moon. 1960 January, G. Freeman Allen, “"Condor"—British Railways' fastest freight train”, in Trains Illustrated, page 48