In the manner of or regarding an altar; in a way that follows the form or orientation of an altar.
From 'altar' + the adverbial suffix '-wise' (like 'lengthwise' or 'clockwise'), meaning in the manner or direction of something.
The '-wise' suffix is surprisingly old and productive in English—you can attach it to almost any noun to create an adverb meaning 'in that manner,' which is why we have 'clockwise' and 'lengthwise.'
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