Толковый словарь английского языка Oxford English Reference - preparatory

adj. & adv. --adj. (often foll. by to) serving to prepare; introductory. --adv. (often foll. by to) in a preparatory manner (was packing preparatory to departure). Phrases and idioms preparatory school a usu. private school preparing pupils for a higher school or US for college or university. Derivatives preparatorily adv. Etymology: ME f. LL praeparatorius (as PREPARE)