In the manner or direction of a gable; in a way that is oriented toward or resembles a gable shape.
From gable + -wise suffix (from Old English wisan, meaning 'direction' or 'manner'). The -wise suffix creates adverbs meaning 'in the manner of' or 'with respect to' (like likewise, otherwise).
The -wise suffix is fading in modern English—we used to say 'clockwise,' 'likewise,' 'lengthwise,' but newer words rarely use it, making gablewise sound archaic even if it technically works.
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