thicken
v.to become more solid or dense. You use this when a liquid like soup or sauce gets thicker as it cooks or when a person's voice changes.
v.to become more dense, viscous, or compact in texture. Often describes the physical change of a liquid or the vocal change in a person's voice.
“The soup will thicken as it cools down.”
“The chef added a bit of flour to the sauce to help it thicken and coat the pasta better.”
“As the storm approached, the atmosphere began to thicken with a sense of impending danger, making the air feel heavy and oppressive to the hikers.”
From Middle English thickenen, thikkenen, perhaps from Old Norse þykkna (“to thicken”); equivalent to thick + -en. Cognate with Swedish tjockna (“to thicken”), Icelandic þykkna (“to thicken”).
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.