Origin and history of recommend

mid-14c., comenden, "praise, mention approvingly," from Latin commendare "to commit to the care or keeping (of someone), to entrust to; to commit to writing;" hence "to set off, render agreeable, praise," from com-, here perhaps an intensive prefix (see com-), + mandare "to commit to one's charge" (see mandate (n.)). A doublet of command.

Sense of "commit, deliver with confidence" in English is from late 14c. Meaning "bring to mind, send the greeting of" is from c. 1400. The "praise" sense is from the notion of "present as worthy of notice or regard;" also in some cases probably a shortening of recommend. Related: Commended; commending.

early 15c., recommendacion, "action of commending oneself to another" (a sense now obsolete), from Old French recommendation (Modern French recommandation), from Medieval Latin recommendationem (nominative recommendatio), noun of action from past-participle stem of recommendare (see recommend). Meaning "act of representing in a favorable manner, act of recommending (someone or something) as worthy" is from 1570s. Letter of recommendation is from c. 1500.

Letter of recommendation, a letter given by one person to another, and addressed to a third or "to whom it may concern," in which the bearer is represented as worthy of consideration and confidence. [Century Dictionary, 1895]