In a manner that can be changed or modified; capable of being altered.
From alterable plus -ly (adverbial suffix). The root Latin alterare meaning 'to change' combines with the Germanic -ly suffix to create an adverb describing how something can be done in an alterable fashion.
Adverbs ending in -ly often feel awkward because we rarely need to describe *how* something changes—but medieval philosophers loved this word when debating whether human nature could be 'alterably' transformed through virtue!
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