resinous

Resinous is an adjective relating to resin, a class of viscous, hydrophobic substances produced by many plants, particularly conifers, as a defensive exudate. It can describe both natural resins and resin-like materials, including certain finishes and synthetic polymers.

Natural resins are complex mixtures of organic compounds, primarily terpenes and other hydrocarbons, often accompanied by non-volatile resin acids. They are typically sticky in fresh form, gradually hardening as they age or oxidize, and they may be soluble in organic solvents while being immiscible with water. The term resinous also extends to describe resins’ characteristic odors—piney, balsamic, or citrusy—and their appearances, which range from transparent to opaque and from gummy to hard solids. In mineralogy, resinous is used to describe a resin-like luster on some minerals.

Natural resins occur as exudates from wounded trees or as secretions of certain plant glands. Historically, they have been used for varnishes, adhesives, caulking, and waterproofing. Rosin (a solid residue obtained from resin) and colophony are well-known examples; amber is fossilized resin. In modern practice, synthetic resins—thermosetting polymers such as phenolic or epoxy resins—are engineered to mimic and extend the properties of natural resins, serving roles in coatings, plastics, and composites.

The term resinous may also describe objects or surfaces containing or resembling resin, or colors and textures reminiscent of resin, including luster or odor characteristics associated with resinous materials.