An adviser or advisor is normally a person with more and deeper knowledge in a specific area and usually also includes persons with cross-functional and multidisciplinary expertise. An adviser's role is that of a mentor or guide and differs categorically from that of a task-specific consultant. An adviser is typically part of the leadership, whereas consultants fulfill functional roles.[1]
The spellings adviser and advisor have both been in use since the 16th century.[2] Adviser has always been the more usual spelling, though advisor has gained frequency in recent years and is a common alternative, especially in North America.[3][4]