Adviser or advisor? It doesn't matter what your computer's spellcheck tells you, adviser and advisor are both correct. Although there is enough overlap between these two words that they are generally considered simply to be different ways to spell the same word, there are some cases in which one tends to be used more often than the other. Some people feel that advisor is more formal, and it tends to be found more often when applied to official positions, such as an advisor to a president. When referring to someone who is serving in a military role, especially when using the term as a euphemism (as when claiming that troops are actually military advisers), then adviser is somewhat more common.