1. Close to; ready to. — Used with an infinitive.
/I haven't gone yet, but I'm about to./
Compare: [GOING TO], [ON THE POINT OF].
2. {informal} Having a wish or plan to. — Used with an infinitive in negative sentences.
/Freddy wasn't about to give me any of his ice-cream cone./
/"Will she come with us?" asked Bill. "She's not about to," answered Mary./