1. Not preventable.

Nuttall's Standard dictionary of the English language By Nuttall, P.Austin

• upreventable,
• unpreasentable,
• unpresentablee,
• unprasentable,
• unpresentible,
• unpresenteble,
• ynpreventable,
• hnpreventable,
• unprevntable,
• unprevetable,
• unprevnetable,
• unprevenatble,
• unpreventablee,
• unprevantable,
• unprevendable,
• unpreventible,
• unpreventeble,
• impr3eventable,
• Unpreventiable,
• Unprevetible

• unforeseen,
• unprintable,
• unpredictably,
• unfrequented,
• unprogressive,
• unforeseeable,
• unparented,
• unapparent,
• unprofitable,
• unprofitableness,
• unpredictable,
• unappareled,
• unprecedented,
• unprofitably,
• unpresidential,
• unpresentable.

The adjective form of "unpreventable" is "unpreventable" itself. The word does not change in form when used as an adjective.

The plural form of the word "unpreventable" is "unpreventables".

The singular form of "unpreventable" is "unpreventable". The word does not change in its singular form, regardless of whether it is used in the singular or plural context.