The word "squaddie" is a slang term commonly used in British English to describe a soldier. However, there are various synonyms that can also be used to refer to a soldier, depending on the context.
One synonym for squaddie is "trooper," which is often used when referring to members of a cavalry unit. Another term that can be used is "grunt," a colloquialism that is often used to describe soldiers in infantry units.
"GI" is another word commonly used to describe American soldiers. In Australian and New Zealand English, soldiers are often referred to as "diggers," while in Canada, they are called "grunts" or "beavers."
Overall, as with any language, there are a variety of words that can be used to describe the same thing. When referring to soldiers, it's important to consider the context and location to determine the most appropriate synonym to use.