ineluctable,certain/inevitable 
inept,unskillful/said or done at the wrong time
infertile,not fertile/barren
infiltrate,to pass into or through/to penetrate sneakily
inflame,become red/angry
inflammatory,tending to inflame
infuriate,fill with fury or rage 
infuse,put/pour/fill
ingenuous,naive/young/artless/frank/honest/sincere
ingest,take in by swallowing
inherent,existing as a natural part
inhibit,hinder/restrain
inimical,harmful or friendly
inimitable,defying imitation/unmatchable 
innocuous,causing no harm
inscrutable,incapable of being discovered or understood 
insensible,unconscious/unresponsive/unaffected 
insinuate,suggest unpleasantly/make a way for smth gently
insipid,without taste or flavour
insouciant,unconcerned/carefree 
insularity,narrow-mindedness/isolated 
insurrection,rising of people to open resistance to
interdict,prohibit/forbid 
interim,as an instalment
intermittent,periodic/on and off
intersperse,place here and there
intervene,come between/interfere to change the result
intractable,unruly/refractory/stubborn 
intransigence,unwillingness to compromise/stubbornness/intractability 
intransigent,uncompromising
intrepid,fearless/brave/undaunted 
introspection,examining one's own thoughts and feelings
inundate,flood/cover by overflowing
inured,accustomed to/adapted 
invective,abusive language/curses
inveigh,to attack verbally/denounce/deprecate 
inveterate,deep-rooted/long-established
involute,complex 
irascible,irritable/easily angered 
irate,angry
ire,anger
irksome,tiresome
irrelevant,not relevant/not connected
irresolute,hesitating/undecided
irreverence,a lack of proper respect
irrevocable,final and unalterable
itinerary,plan for a journey/details or records of a route
itinerate,to travel from place to place/to peregrinate 
jabber,talk excitedly/utter rapidly
jeopardize,put in danger