in terms of depth or according to depth; with respect to how deep something is.
From 'depth' plus '-wise' (from Old English 'wisa' meaning manner or fashion). The '-wise' suffix means 'in the manner of' or 'with respect to.'
The suffix '-wise' is a clever linguistic shortcut: clockwise, likewise, depthwise—it transforms nouns into adverbs that mean 'in the manner/direction/respect of' that noun, letting us modify almost any word!
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