Tending to cause deformation; having the quality or effect of deforming or changing shape.
From deform + -ative (suffix creating adjectives meaning 'tending to' or 'having the quality of'). The -ative suffix comes from Latin -ativus.
High heat can have a deformative effect on plastic objects—this is why you shouldn't leave plastic containers in a hot car; the heat literally reshapes them.
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