I've read the entire series of Culture novels and don't recall seeing "starmind" as a term anywhere. Mind, yes, but used in a somewhat different context, as the minds are both sentient conversational AI entities with equal or greater intellect to a meat-based human or alien, and also semi-godlike AI powers (a single Mind has the capacity to have a 1:1 conversation with all of the residents of an Orbital if it wants to).