Select the most appropriate one-word substitution for the given group of words.

One who changes sides

turncoat

The most appropriate one-word substitution for one who changes sides is turncoat.

• Invader is a person who enters a country or territory illegally or without permission.
• Novice is a person who is new to a particular activity or field.
• Amateur is a person who engages in an activity for pleasure rather than as a profession.