Unbidden a. : Not bidden; not commanded.

Unbidden a. : Uninvited; as, unbidden guests.

Unbidden a. : Being without a prayer.

Example:
has anyone ever had Norton install itself on their PC Unbidden?

Taxonomy
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Defination from the web:
unbidden from the Merriam-Webster Online Dictionary with audio pronunciations, thesaurus, Word of the Day, and word games. ... See a map of "unbidden" in the Visual Thesaurus. Pronunciation Symbols. Share this entry: Link to this page: Cite this page: Products. Premium Services ...