1.isotope n．同位素(兩個或更多具有相同原子序數卻具有不同的質量數的原子中的一個)(one of two or more atomic number but different mass numbers)

詞根記憶：iso(等，同)+tope--同位素

例：heavy isotope重同位素

派生詞：isotopic(a．同位素的)

2.jeopardize v.危及，危害(to expose to danger or risk)

詞根記憶：jeopard (危險)+ize--使處于危險中--危及，危害

例：If too little attention is given to basic research today, future technological advancement will be jeopardized.

派生詞：jeopardy(n.危險，危害)

3.judicial a．司法的(of, relating to, or proper to courts of law or to the administration of justice)；公正的(just)

詞根記憶：judic（評判，法律）+ial--司法的；公正的

例：judicial rules司法規定

4.jumbo a．巨大的(unusually large)

聯想記憶：本是一頭大象的名字，代指“體大而笨拙的人”，作形容詞用時意為“巨大的”

例：The development of a new jumbo rocket is expected to carry the U.S. into its next phase of space exploration.

5.jurisdiction n.管轄權(authority or control);管轄區域(the limits within which authority may be exercised)

詞根記憶：juris(=jury法律）+dict(命令)+ion--按照法律享有命令權--管轄權

例：These islands are under U.S. jurisdiction. //One state adds a 7 percent sales tax to the price of most products purchased within its jurisdiction.

6.juror n.陪審團成員(a member of a jury)

詞根記憶：jur(評判，法律)+or--按照法律評判的人--陪審團成員

例：Civil trials often involve great complexities that are beyond the capacities of jurors to understand.

7.justify v.證明…正當或有理(to prove or show to be just, right, or reasonable)

詞根記憶：just(正義)+ify(使…)葉證明…正當（或有理）

例：Companies are never justified in employing young children, even if the child's family would benefit from the income.

派生詞：justification(n．正當理由：辯護)：justifiably（ad.有理由地）：unjustified（a．未被證明正確的）

8.juvenile a．青少年的(youthful)

詞根記憶：juven(年青)+ile --青少年的

例：Juvenile delinquency is a serious social problem.

同根詞：rejuvenate(v.返老還童)

9.juxtapose v.并放，并列(to place side by side)

詞根記憶：juxta(接近)+pose(放)--挨著放--并放，并列

例：The central idea is restated and juxtaposed with evidence that might appear to contradict it.

10.kernel n.果仁(the inner part of a nut or seed)；核心(most important part)

詞根記憶：kern( =corn種子)+el--核心

例：Heating a wheat kernel destroys its gluten , a protein that must be present in order for yeast to leaven bread dough.

11.kidney n．腎臟

例：Desert rats' kidneys can excrete a urine having twice as high a salt content as sea water.

12.kin n.<集合詞>家屬，親戚(relatives)

例：Self-help and the help of kin got most workers through jobless spells.

派生詞：kinship(n.親屬關系)

13.kinetic a.運動的(of, relating to, or produced by motion)

詞根記憶：kinet(動)+ic--運動的

例：kinetic energy動能

同根詞：kinescope(n.顯像管);kinematics(n．運動學)