Pact

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late Middle English: from Old French, from Latin pactum ‘something agreed’, neuter past participle (used as a noun) of paciscere ‘agree’.

wiktionary

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From Middle French pacte, from Old French, from Latin pactum(“something agreed upon”), from paciscere(“to agree”).

etymonline

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pact (n.)

"an agreement between persons or parties," early 15c., from Old French pacte "agreement, treaty, compact" (14c.) and directly from Latin pactum "agreement, contract, covenant," noun use of neuter past participle of pacisci "to covenant, to agree, make a treaty," from PIE root *pag- "to fasten." Related: Paction "act of making a pact."