'Promise' is Latin for 'send forth one's word' — from the vast 'mittere' family of mission and missile.
A declaration that one will do or refrain from doing something; to assure someone that one will definitely do something or that something will happen.
From Old French 'promesse' and Medieval Latin 'promissa' (a promise, a declaration sent forward), noun from the feminine past participle of Latin 'prōmittere' (to send forth, to let go forward, to pledge), composed of 'prō-' (forward, forth, into the future) + 'mittere' (to send, to let go, to throw). The PIE root behind 'mittere' is *mey- (to throw, to cast), though 'mittere's full prehistory remains debated. The spatial and temporal metaphor embedded in 'promise' is exact: to promise is to project
A 'promise' is literally something 'sent forward' — your word projected into the future. The same root 'mittere' (to send) lives in 'missile' (something sent flying), 'mission' (a sending), and 'message' (something sent). Every promise is, etymologically, a word you launch ahead of yourself and then must chase down