1. two words that can be interchanged in a context are said to be synonymous relative to that context
2. One of two or more words (commonly words of the same language) which are equivalents of each other; one of two or more words which have very nearly the same signification, and therefore may often be used interchangeably. See under Synonymous.
3. An incorrect or incorrectly applied scientific name, as a new name applied to a species or genus already properly named, or a specific name preoccupied by that of another species of the same genus; -- so used in the system of nomenclature (which see) in which the correct scientific names of certain natural groups (usually genera, species, and subspecies) are regarded as determined by priority.