Definition
A property of certain fluids and gels that causes them to become less viscous (thinner and more flowable) when stirred, shaken, or otherwise agitated, and to return to their thicker state when allowed to stand undisturbed.
Plain English
A thixotropic substance is thick when it sits still and turns runny when you stir or shake it. Leave it alone for a while and it firms up again.
Context Anchor
Seen in aircraft maintenance discussions of sealants, adhesives, greases, and coatings.
Derivation
From the Greek 'thixis' meaning 'touching' and 'tropos' meaning 'turning' or 'change.' Literally 'change by touching' -- which captures the idea exactly: touch it (stir or shake it) and it changes how it flows.
Why Pilots Care
Thixotropic behavior matters when applying sealants, greases, or paints during maintenance. The product flows easily while being worked but stays in place once applied, which affects how surfaces are prepared and how cure times are managed.
Analogy
Think of ketchup in a glass bottle. It sits like a solid until you shake it, then flows freely; left alone, it thickens again.
Intuition Check
Thixotropic does not simply mean “thick.” It means the material changes how easily it flows depending on whether it is being worked or left still.
Example Sentence 1
The mechanic chose a thixotropic sealant so it would stay in place on the vertical seam without sagging after application.
Example Sentence 2
Thixotropic properties allow the sealant to be easily applied during installation yet resist migration once cured.