Ambiguous @ Used to indicate when something is ambiguous
Mistake @ something done incorrectly, such as a mispelling.
vain @ used to indicate when a certain task is being performed with no possibility of success, and with a high rate of errors. For example, asking members of a forum to provide definitions for arbitrary words. the resultset will likely only contain those words used in that particular area; and possiblity with many mistakes and/or self-representing definitions.