The property or tendency of something to expand, especially the measurable rate at which a material increases in volume when heated.
From expansive plus the suffix '-ity' (forming abstract nouns from adjectives). Used especially in physics and materials science since the 18th century.
Expansivity is why bridges and railroad tracks have tiny gaps built into them—metal expands when warm and contracts when cold, and engineers must calculate exactly how much using the material's coefficient of thermal expansivity. This is why old structures sometimes buckle in summer heat.
Complete word intelligence in one call. Free tier — 50 lookups/day.