False synonym refers to words that appear to have similar meanings but differ in nuance, context, or usage, potentially leading to misunderstanding. These are also called pseudo-synonyms.

For example:

• Big and large are often used interchangeably, but big can sound more informal, while large feels more formal.

• Flammable and inflammable both mean "capable of catching fire," despite the prefix in- usually suggesting negation—this can cause confusion in safety contexts.

• Sanction can mean either to approve or to punish, depending on context, making it a risky word in contracts or legal writing.

Using false synonyms can alter tone, intent, or meaning. Always consider context and consult a dictionary or thesaurus to ensure precision in communication.