Question: is oh electrophile or nucleophile?
Answer: When hydroxide ion donates a pair of electrons to an electrophilic atom (such as carbon here) to form a new covalent bond, it is acting as a nucleophile. And as we've seen before, when hydroxide ion donates a pair of electrons to an (acidic) proton to form a new covalent bond, we say it's acting as a “base“.