from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A subdivision of a field of study; a subdiscipline.
- n. Mathematics A field that is a subset of another field.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A smaller, more specialized area of study or occupation within a larger one
- n. A subring of a field, containing the multiplicative identity and closed under inversion.
sub- + field (Wiktionary)