Impracticable means (of a course of action) impossible in practice to do or carry out. Fastidious means hard to please. Inaccessible means unable to be approached. Indefatigable means unable to be tired.

Fastidious means very attentive to and concerned about accuracy and detail; hard to please. Impracticable means impossible to practice. Inexpressible means unable to be expressed. Indeterminable means unable to be fixed.

Imperceptible means so slight, gradual, or subtle as not to be perceived. Inconceivable means impossible to imagine. Incomprehensible means impossible to understand. Inexpressible means unable to be expressed.

Incomprehensible means not able to be understood; not intelligible. Inconceivable means impossible to imagine. Imperceptible means unable to be perceived. Impracticable means impossible to put into practice.

Inconceivable means not capable of being imagined or grasped mentally; unbelievable. Incomprehensible means impossible to understand. Imperceptible means unable to be perceived. Fastidious means hard to please.

Invulnerable means impossible to harm or damage. Invincible means unable to be conquered. Impregnable means unable to be seized. Imperceptible means unable to be perceived by the senses.

Impregnable means (of a fortified position) unable to be captured or broken into. Invincible means unable to be conquered. Invulnerable means impossible to harm. Incomprehensible means impossible to understand.

Invincible means too powerful to be defeated or overcome. Impregnable means unable to be seized or captured. Invulnerable means impossible to harm or wound. Inconceivable means impossible to imagine.

Incredible means difficult or impossible to believe. Inaudible means unable to be heard. Illegible means unreadable. Indelible means unable to be removed.

Indelible means (of ink or a pen) making marks that cannot be removed. Inaudible means unable to be heard. Illegible means unreadable. Incredible means unable to be believed.