Iatromathematician (n.)
definition: One of a school of physicians in Italy
About the middle of the 17th century who tried to apply the laws of mechanics and mathematics to the human body and hence were eager student of anatomy; -- opposed to the iatrochemists.
Iatromathematician is an 18 letter word that begins with an I and ends in an N

Impracticabilities (pl)
definition: of Impracticability

Impracticabilities is an 18 letter word that begins with an I and ends in an S

Imprescriptibility (n.)
definition: The quality of being imprescriptible.

Imprescriptibility is an 18 letter word that begins with an I and ends in a Y

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

Impressionableness is an 18 letter word that begins with an I and ends in an S

Incircumscriptible (a.)
definition: Incapable of being circumscribed or limited.

Incircumscriptible is an 18 letter word that begins with an I and ends in an E

Incommensurability (n.)
definition: The quality or state of being incommensurable.

Incommensurability is an 18 letter word that begins with an I and ends in a Y

Inconsequentiality (n.)
definition: The state of being inconsequential.

Inconsequentiality is an 18 letter word that begins with an I and ends in a Y

Indecomposableness (n.)
definition: Incapableness of decomposition; stability; permanence; durability.

Indecomposableness is an 18 letter word that begins with an I and ends in an S

Ineffervescibility (n.)
definition: The quality of being ineffervescible.

Ineffervescibility is an 18 letter word that begins with an I and ends in a Y

Insurmountableness (n.)
definition: The state or quality of being insurmountable; insurmountability.

Insurmountableness is an 18 letter word that begins with an I and ends in an S

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