Preparing for something; introductory; preliminary.
- Nuttall's Standard dictionary of the English language. By Nuttall, P.Austin. Published 1914. (adjective) (adj.) (adjective)
Serving to make ready or to fit for something further; being fitted or made ready, as by instruction.
- The Winston Simplified Dictionary. By William Dodge Lewis, Edgar Arthur Singer. Published 1919. (adjective) (adj.) (adjective)
Previously necessary; introductory; preliminary.
- Etymological and pronouncing dictionary of the English language. By Stormonth, James, Phelp, P. H. Published 1874. (adjective) (adj.) (adjective)
Preparing for: previous: introductory: preparative.
- The american dictionary of the english language. By Daniel Lyons. Published 1899. (adjective) (adj.) (adjective)
Preparing; introductory.
- The Clarendon dictionary. By William Hand Browne, Samuel Stehman Haldeman. Published 1894. (adjective) (adj.) (adjective)

Usage examples:

Next morning he was standing in the hall preparatory to going out, when his servant approached him and handed him a note.
- The Red Rat's Daughter by Guy Boothby
Ere long his activities might be curtailed, for he was threatened with a preparatory school in the autumn; but before that happened, the Red Hand must be set in certain high places, and the hackling shop of Levi Baggs was first among them.
- The Spinners by Eden Phillpotts
The Skanderbeg military school is a secondary or preparatory school.
- Area Handbook for Albania by Eugene K. Keefe Sarah Jane Elpern William Giloane James M. Moore, Jr. Stephen Peters Eston T. White