To make gross, coarse, or crude; to enlarge or increase in size or magnitude.
From 'gross' plus Latin '-ify' (to make), a rarely-used verb form that follows the standard pattern of creating action words from adjectives.
Medieval English loved creating verbs by adding '-ify' to adjectives, which is why we can theoretically 'grossify' things—but this particular verb never caught on in everyday speech!
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