Using all letters

                                                                            iniquitous

                                                                            inquisition

                                                                           inquisitions

                                                                          The other words:

                                                                            institution

                                                                           institutions

                                                                             intuition

                                                                            intuitions

                                                                              intuito

                                                                               ninon

                                                                             nonunion

                                                                            nonunionist

                                                                             nonunions

                                                                               noons

                                                                              notion

                                                                              notions

                                                                               nouns

                                                                               onion

                                                                              onions

                                                                               ousts

                                                                               quito

                                                                               quoin

                                                                              quoins

                                                                               quoit

                                                                              quoits

                                                                              sinuous

                                                                               snoot

                                                                              snoots

                                                                               snots

                                                                               snout

                                                                              snouts

                                                                               soots

                                                                               stout

                                                                              stouts

                                                                               toots

                                                                               touts

                                                                              tuition

                                                                             tuitions

                                                                               union

                                                                             unionist

                                                                             unionists

                                                                              unions

                                                                              unison

                                                                              unisons