Source : WordNet®

jack oak
     n 1: a common scrubby deciduous tree of central and southeastern
          United States having dark bark and broad 3-lobed
          (club-shaped) leaves; tends to form dense thickets [syn:
           {blackjack oak}, {blackjack}, {Quercus marilandica}]
     2: small to medium deciduous oak of east central North America;
        leaves have sharply pointed lobes [syn: {northern pin oak},
         {Quercus ellipsoidalis}]