Princeton's WordNet

1. blackjack oak, blackjack, jack oak, Quercus marilandica(noun)

   a common scrubby deciduous tree of central and southeastern United States having dark bark and broad three-lobed (club-shaped) leaves; tends to form dense thickets

2. jack oak, northern pin oak, Quercus ellipsoidalis(noun)

   small to medium deciduous oak of east central North America; leaves have sharply pointed lobes