In a slanting or diagonal manner; following a slanted direction or course.
Combination of 'aslant' plus the suffix '-wise' (meaning 'in the manner of' or 'direction of'). The '-wise' suffix comes from Old English 'wisan' meaning 'way' or 'manner,' and was productive in creating adverbs throughout English history.
The '-wise' suffix was wildly popular for making directional adverbs (likewise, clockwise, lengthwise), but 'aslantwise' is so rare that most modern dictionaries don't even include it—it's a word that lost the linguistic lottery.
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