prep·py or prep·pie 
(prĕpē) Informal
(prĕpē) Informal n. pl. prep·pies
1. A student or former student of a preparatory school.
2. A person whose manner and dress are deemed typical of traditional preparatory schools.
adj. prep·pi·er, prep·pi·est
Of or relating to a preppy or a preparatory school.
[PREP(ARATORY SCHOOL) + -Y1.]
preppi·ly adv.
preppi·ness n.