/ ˌɪnvəˈkeɪʃn; NAmE / noun [ U , C ]
1.
( formal ) the act of asking for help, from a god or from a person in authority; the act of referring to sth or of calling for sth to appear
2.
( computing ) the act of making a particular function start
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WORD ORIGIN
late Middle English : via Old French from Latin invocatio(n-) , from the verb invocare , from in- upon + vocare to call.