1. So as to preclude doubt.

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

• demonsrtrably,
• demonstably,
• demonstratably,
• demostrably,
• semonstrably,
• xemonstrably,
• cemonstrably,
• femonstrably,
• remonstrably,
• eemonstrably,
• dwmonstrably,
• dsmonstrably,
• ddmonstrably,
• drmonstrably,
• d4monstrably,
• d3monstrably,
• denonstrably,
• dekonstrably,
• dejonstrably,
• deminstrably

• demonstrated,
• demonstrative,
• demonstration,
• demonstrable,
• demonstrability,
• demonstratively,
• demonstrate,
• demonstrator.

The adjective form of the word "demonstrably" is "demonstrable".

The plural form of the word "demonstrably" is "demonstrablys". However, it is worth mentioning that "demonstrablys" is a rarely used form and it is more common to use the word in its singular form regardless of the subject-verb agreement.

The singular form of the word "demonstrably" is "demonstrable"