The spelling of the word "Addamson" follows English pronunciation rules. It is pronounced as /ædəmsən/, with emphasis on the first syllable "AD". The "dd" sound represents a double-consonant sound commonly used in English to indicate a stressed syllable and it is followed by the letter "a". The letter "o" is pronounced as "uh" and "n" at the end is said with the "n" sound. Therefore, the correct spelling of this surname is "Addamson".