An adviser or advisor is often someone who has more and more in-depth knowledge in a certain field, and it typically also includes someone who have competence in both cross-functional and interdisciplinary areas. As compared to the job of a consultant who specialises in a certain activity, the function of an advisor is more akin to that of a teacher or leader. The job of an advisor is often that of a member of the leadership, while the responsibilities that consultants play are more functional.
Adviser was first recorded in English in the 12th century. While the spelling advisor has become increasingly frequent in recent years and is now a common option, the more traditional form of the word is still adviser. This is notably true in North America.