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1.ICONOCLAST: one who opposes established beliefs , customs and institutions

similar meanings: MAVERICK        NONCONFORMIST     REVOLUTIONARY

2.IMPERTURBABLE: not capable of being disturbed

similar meanings: DISPASSIONATE     SERENE     STOICAL      IMPASSIVE

3.IMPERVIOUS: impossible to penetrate

similar meanings: RESISTANT        IMPREGNABLE

4.IMPETUOUS: quick to act without thinking

similar meanings: IMPULSIVE      PRECIPITATE     RECKLESS      SPONTANEOUS

5.IMPLACABLE: unable to be calmed down  or  made peaceful

similar meanings:  REMORSELESS        INEXORABLE      INTRANSIGENT    
                               RELENTLESS            UNFORGIVING

6.INCHOATE: not fully formed , disorganized

similar meanings: AMORPHOUS      UNORGANIZED   INCOHERENT

7.INGENUOUS: showing innocence or childlike simplicity

similar meanings: ARTLESS        INNOCENT      GUILELESS     NAIVE

8.INIMICAL: hostile , unfriendly

similar meanings: RECALCITRANT     DISSIDENT     ANTAGONISTIC       ADVERSE

9.INNOCUOUS: harmless

similar meanings: BENIGN        INOFFENSIVE      

10.INSIPID: lacking interest  or   flavor

similar meanings:  BANAL      BLAND      STALE      VAPID      DULL  

11.INTRANSIGENT: uncompromising , refusing to be reconciled

similar meanings: IMPLACABLE      UNBENDING      INEXORABLE     IRRECONCILABLE
                              OBDURATE           UNRELENTING

12.INUNDATE:  to overwhelm , to cover with water

similar meanings: DELUGE       DROWN      ENGULF         FLOOD       SUBMERGE

13.IRASCIBLE: easily made angry

similar meanings:  CANTANKEROUS     ORNERY        TESTY      IRRITABLE