What's an intuitive derivation behind ODO's definition that helps to remember its meaning:
undertake = [with object] 1. Commit oneself to and begin (an enterprise or responsibility); take on:
Etymonline: c.1200, "to entrap;" c.1300, "to set about (to do)," from under + take (v.). Similar formation in French entreprendre "to undertake," from entre "between, among" + prendre "to take." The under in this word may be the same one that also may form the first element of understand. Old English had underniman "to trap, accept" (cognate with Dutch ondernemen, German unternehmen).
How does the prefix under- mean 'on'? Etymonline mentions the French entreprendre, but how does this help? First, entre- is a different preposition. Second, I also don't understand how 'between/among + take' evolves into 'take on' ? I tried Etymonline's page on under- to no avail, esp. because it refers to other languages. Is there a simpler, more intuitive explanation?