1. To dispatch a request for someone or something to be ready or available by the time that one arrives. The conductor of the train sent ahead for a doctor to meet them at the next station to treat the ill passenger. I always send ahead for a limo to pick me up from the airport whenever I fly.

2. To direct someone to travel ahead in order to bring back or make ready or available someone or something. In this usage, a noun or pronoun is used between "send" and "ahead." I sent my assistant ahead for lunch reservations at the hotel. The whole unit was moving slower due to the lieutenant's injuries, so they sent me ahead for help.