natural action vs stiffening

Other hyponyms of natural action include radiation, absorption, acidification, adiabatic process, aeration, antiredeposition, capture, capture, centrifugation, chemical action, chemical change, chemical process, chromatography, concretion, condensation, convection, clotting, coagulation, curdling, decay, demagnetisation, demagnetization, desorption, diffusion, disintegration, dissolution, distillation, distillment, drift, effervescence, cataphoresis, dielectrolysis, electrophoresis, ionophoresis, ecesis, establishment, extinction, extraction, feedback, filtration, flocculation, flow, formation, fossilisation, fossilization, geologic process, geological process, curing, hardening, set, solidification, solidifying, inactivation, ion exchange, ionisation, ionization, leach, leaching, magnetic induction, magnetisation, magnetization, materialisation, materialization, nuclear reaction, opacification, oscillation, oxygenation, pair creation, pair formation, pair production, phase change, phase transition, physical change, state change, precession of the equinoxes, release, saltation, scattering, sericulture, sink, soak, soakage, soaking, softening, sorption, source, rigidification, rigidifying, stimulation, ecological succession, succession, natural selection, selection, survival, survival of the fittest, synergism, synergy, temperature change, transduction, transpiration, vitrification.