Wiktionary
vb. (context transitive English) To move back from a flexed position.
Usage examples of "unflex".
I fought to unflex my fingers, break the hold they kept upon the crystal hilt, which was no longer clouded, as it had been when first I found it, but rather shone with that sparkling of light which had fired up in it when the blade had been once more fitted to the grip.
Teblor endeavoured to keep his muscles fit through sessions, late at night, of flexing and unflexing, but all his joints ached from immobility, and for this he could do nothing.
He lumbered toward Bethom, flexing and unflexing his fingers, clearly ready to break Bethom in half the moment he got his hands on him.
He was the last in the line of defeated wizards, yet he carried himself with a haughty swagger, flexing and unflexing his giant claws dramatically.