Merriam-Webster's Collegiate Dictionary:
aplastic anemia
aplenty
aplite
aplitic
aplomb
apnea
apneic
apnoea
apo
apo, mount
apo-
apoc
apocalypse
apocalyptic
apocalyptical
apocalyptically
apocalypticism
apocalyptism
apocalyptist
apochromatic
apocope
apocrine
apocrypha
apocryphal
apocryphally
apocryphalness
apodeictic
apodictic
apodictically
apodosis
apoenzyme
apogamy
apogean
apogee
apolipoprotein
apolitical
apolitically
apoliticism
apollinaire
apollinian
apollo
apollonian
apollonius
apollyon
apologetic
apologetically
apologetics
apologia
apologia pro vita sua
apologise
apologist
apologize
apologizer
apologue
apology
apolune
apomict
apomictic
apomictically
apomixis
apomorphine
aponeurosis
aponeurotic
apophasis
apophthegm
apophyllite
apophyseal
apophysis
apopka
apoplectic
apoplectically
apoplexy
apoptosis
apoptotic
aporia
aport
apos
aposematic
aposematically
aposiopesis
aposiopetic
apospory
apostasy
apostate
apostatise
apostatize
apostle
apostles' creed
apostleship
apostolate
apostolic
apostolic delegate
apostolic father
apostolicity
apostrophe
apostrophic
apostrophise
