A C172 pilot departing a non-towered airport reported they rejected takeoff to avoid a helicopter departing in front of them from a taxiway.

Narrative

Today; I was practicing pattern work with a student pilot. I was holding short of Runway XX on Taxiway 1. There was a Cessna 172 turning left downwind to base; a Cessna 172 on the departure leg of XX; and a Helicopter with its engine running on taxiway 2 by the FBO. The helicopter was on the ground. I made a call over the radio that we were going to depart XX and remain in the pattern. As we were on our takeoff roll about to lift off; I saw the helicopter lift off and cut across the runway. I aborted the takeoff and called that we aborted the takeoff over the radio. I then asked the helicopter what he was doing over the radio; and his transmission was weak and difficult to hear. When they saw us; they backed up to Taxiway 2 and then continued forward. They were able to move out of the way; and we cleared the Runway via [Taxiway] 2. The Cessna in the pattern had to do a right 360. The helicopter departed the area; and we taxied back to XX. We then took off and departed the area to the South East; back to ZZZ. I asked UNICOM for the helicopter's tail number; and the pilot of the helicopter called to say that he was still on the frequency and asked for my phone number. After landing I called the FBO and talked with a customer service representative who had witnessed the incident. They relayed that they heard the helicopter call that he was going to depart; and said they also heard me call that I was going to depart. They clarified that they believed the helicopter said he would depart parallel to the runway and did not expect him to go across the runway. The helicopter pilot called me around XA00 and discussed what happened. We both concluded that we did not hear each other's calls and that we would be more attentive next time.