What is the difference between a base and a nucleophile?
Nucleophiles are technically defined to be lewis bases, but organic chemists tend to differentiate between them via their behavior.
A Lewis base is an electron donor, and a Brønsted-Lowry base is a proton acceptor. A Lewis base that acquires a proton as a result of donating electrons is thus also a Brønsted-lowry base. When that occurs, it is said to be basic behavior.
A nucleophile is also an electron donor, but strictly speaking, if it donates electrons to make a bond with a non-proton, then it is said to be nucleophilic behavior.