1: one of two or more words or expressions of the same language that have the same or nearly the same meaning in some or all senses

2 : a word or phrase that by association is held to embody something (as a concept or quality)

Dumbass or Asshole
(a word you can say without saying a curse and it will confuse the hell out of anyone who dosent know what it means)

One of the functions most missing in Urbandictionary.com

word meaning similar to another word

this is another stuffy professor word. its basically stuffy old man way to say aka

1. A word that means the same, or almost the same, as another word in the same language, either in all of its uses or in a specific context.

2. a word or expression that is used as another name for something in some styles of speaking or writing or to emphasize a specific aspect or association.

3. A duplicate taxonomic name that has been rejected or replaced.

A word you use when you don't know how to spell the first one.