Iatromathematical (a.)
definition: Of or pertaining to iatromathematicians or their doctrine.

Iatromathematical is a 17 letter word that begins with an I and ends in an L

Ichthyophthalmite (n.)
definition: See Apophyllite.

Ichthyophthalmite is a 17 letter word that begins with an I and ends in an E

Impersonification (n.)
definition: The act of impersonating; personification; investment with personality; representation in a personal form.

Impersonification is a 17 letter word that begins with an I and ends in an N

Impertransibility (n.)
definition: The quality or state of being impertransible.

Impertransibility is a 17 letter word that begins with an I and ends in a Y

Impracticableness (n.)
definition: The state or quality of being impracticable; impracticability.

Impracticableness is a 17 letter word that begins with an I and ends in an S

Impressionability (n.)
definition: The quality of being impressionable.

Impressionability is a 17 letter word that begins with an I and ends in a Y

Incircumscription (n.)
definition: Condition or quality of being incircumscriptible or limitless.

Incircumscription is a 17 letter word that begins with an I and ends in an N

Incommunicability (n.)
definition: The quality or state of being incommunicable
Or incapable of being imparted.
Incommunicability is a 17 letter word that begins with an I and ends in a Y

Incompressibility (n.)
definition: The quality of being incompressible
Or incapable of reduction in volume by pressure; -- formerly supposed to be a property of liquids.
Incompressibility is a 17 letter word that begins with an I and ends in a Y

Inconsecutiveness (n.)
definition: The state or quality of not being consecutive.

Inconsecutiveness is a 17 letter word that begins with an I and ends in an S

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