suppositive

American Heritage® Dictionary of the English Language, Fourth Edition

1. adj. Of the nature of, including, or involving supposition.
2. n. Grammar A conjunction, such as if or providing, that introduces a supposition.

Century Dictionary and Cyclopedia

1. Supposed; including or implying supposition.
2. n. A conditional or continuative conjunction, as if, granted, provided.

Wiktionary

1. n. A word denoting or implying supposition.

GNU Webster's 1913

1. adj. Including or implying supposition, or hypothesis; supposed.
2. n. A word denoting or implying supposition, as the words if, granting, provided, etc.