To call upon or appeal to (a god, spirit, or authority); to quote or reference something as evidence or justification.
From Latin 'invocare' (in- 'in' + vocare 'to call'), literally meaning to call upon; used in religious contexts for centuries, then expanded to legal and rhetorical uses.
Lawyers love the word 'invoke' when referencing laws, and priests use it calling upon divine help—both are literally using the original Latin meaning of 'calling upon' a higher power to back them up.
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