- Of or relating to a mental faculty. (adjective)
- Capable of occurring or not occurring; contingent. (adjective)
- Not required or compulsory; optional. (adjective)
- Granting permission or authority. (adjective)
- Biology Capable of functioning under varying environmental conditions. Used of certain organisms, such as bacteria that can live with or without oxygen. (adjective)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.