en·gi·neer / ˌenjəˈni(ə)r/ • n. a person who designs, builds, or maintains engines, machines, or public works. ∎  a person qualified in a branch of engineering, esp. as a professional: aeronautical engineer. ∎  the operator or supervisor of an engine, esp. a railroad locomotive or the engine on an aircraft or ship. ∎  a skillful contriver or originator of something: the prime engineer of the approach.• v. [tr.] design and build (a machine or structure): the men who engineered the tunnel. ∎  skillfully or artfully arrange for (an event or situation) to occur: she engineered another meeting with him. ∎  modify (an organism) by manipulating its genetic material: genetically engineered plants.

engineer designer or constructor of engines or works, orig. of military engines. XIV. ME. engineor, -our — OF. engignëor, -our (mod. ingénieur) :- medL. ingeniātor, -ōr-, f. ingeniāre, f. ingenium ENGINE. The ending was later assim. to -ier, -EER1.
Hence engineer vb. intr. XVII; tr. XIX.