Endeavor
late Middle English (in the sense ‘exert oneself’): from the phrase put oneself in devoir ‘do one's utmost’ (see devoir).
wiktionary
The verb is from Middle English endeveren(“to make an effort”); the noun is from Middle English endevour, from the verb. Endeveren is from (putten) in dever(“(to put oneself) in duty”), from in + dever(“duty”), partially translating Middle French(se mettre) en devoir (de faire)(“(to make it) one's duty (to do), to endeavour (to do)”) (from Old French devoir, deveir(“duty”)).
etymonline
endeavor (n.)
early 15c., "pains taken to attain an object," literally "in duty," from phrase put (oneself) in dever "make it one's duty" (a partial translation of Old French mettre en deveir "put in duty"), from Old French dever "duty," from Latin debere "to owe," originally, "keep something away from someone," from de- "away" (see de-) + habere "to have" (from PIE root *ghabh- "to give or receive"). One's endeavors meaning one's "utmost effort" is from late 15c.
endeavor (v.)
c. 1400, from phrase put in dever (see endeavor (n.)). Related: Endeavored; endeavoring.
