Adviser and advisor are different spelling variations of the same word. They both refer to someone who advises and counsels.
"One of the reasons why English spelling is so unpredictable is because itsvocabularyconsists of many words derived from other languages, which have been adopted with their original spellings intact. Understanding the origins of these words and the languages they have come from will help help with...
The chart below is a Google Ngram showing the comparative frequency, in books published in America between 1900 and 2008, of adviser (blue line) and advisor (red line). The -or spelling pulls ahead in about 1999. (In Britain, -er is still ahead though its lead is fading.) Ngram’s...