Incandescent (adj) : brilliant, giving off heat or light

Jan’s ideas were so incandescent that simply being near her made you feel as though you understood the subject for the first time.

Incantation (n) : a chant, the repetition of statements or phrases in a way reminiscent of a chant

The students quickly became deaf to the principal’s incantations about the importance of school spirit.

Incense(v) to make very angry

Jeremy was incensed when I told him that even though he was stupid and Loathsome, he would always be my best friend

Incessant (adj_ unceasing

The noise from the city street was incessant ; there always seemed to be a fire engine or a police car screaming by.

Incipient ( adj) beginning, emerging

Support for the plan was incipient, and the planners hoped it would soon grow and spread.

The inception of something is its start or formal beginning.

Incisive (adj) cutting right to the heart of the matter.

After hours of debate, Luisa offered a few incisive comments that made it immediately clear to everyone how dumb the original idea had been.

Incongruous (adj)  not harmonious; not consistent; not appropriate; not fitting in

Bill’s membership in the motorcycle gang was incongruous with his mild personality and his career as a management consultant.

Incorrigible ( adj) incapable of being reformed

Bill is incorrigible he eats three bags of potato chips every day even though he knows that eating two would be better for him.

Increment (n) an increase; one is a series of increase

This year’s fund-raising total represented an increment of 1 Percent over last year’s.

Incremental-Incrementally

Indifferent ( adj) not caring one way or the other, apathetic mediocre

The painter did an indifferent job, but it was good enough for Susan, who was indifferent about painting.

Mediocre (adj): ordinary, common, indifferent, average

He is an enthusiastic if mediocre painter.