Ad hoc(adjective)
Meaning: created or done for a particular purpose as necessary.
Hindi meaning:तदर्थ, अपूर्वचिन्तित
Synonyms: Unplanned, Impromptu, Improvised, Extemporized
Antonyms: Planned, Prearranged, Premeditated, Organized
Example: The Council meets on an ad hoc basis to discuss problems.
Trick to remember: add a clock(time alarm) for unplanned meeting









