1. As far as is related to, regards, or concerns someone; to the degree that someone is involved or a part of something. On the part of the employees, the company's merger means that many will be losing their jobs. On the part of Jane and Melissa, they have been instrumental in getting this project off the ground.

2. As comes from or is done by someone. Guarantees on the part of the banks must be made to assure the country's citizens that their money is safe during this period of recovery. There has been no shortage of effort on the part of John to make sure that this campaign is a success.