We found 10 dictionaries that define the word empty set:

General (4 matching dictionaries)

1. empty set: Wiktionary
2. empty set: Dictionary.com
3. Empty set, The empty set: Wikipedia, the Free Encyclopedia
4. empty set: TheFreeDictionary.com

Computing (1 matching dictionary)

5. empty set: Encyclopedia

Miscellaneous (1 matching dictionary)

6. Encyclopedia of Graphic Symbols (No longer online)

Science (3 matching dictionaries)

7. A Glossary of Mathematical Terms (No longer online)
8. Empty Set: Eric Weisstein's World of Mathematics
9. empty set: PlanetMath Encyclopedia

Slang (1 matching dictionary)

10. empty set: Urban Dictionary

Definitions from Wiktionary (empty set) ▸ noun:  (set theory) The unique set that contains no elements, denoted ∅ or {}. Similar: null sign, empty function, null set, absolute complement, singleton set, zero, uncountable set, disjoint set, ideal, connection, more... Opposite: non-empty set, populated set, set with elements Phrases: Axiom of empty set, more... ▸ Words similar to empty set ▸ Usage examples for empty set ▸ Idioms related to empty set ▸ Wikipedia articles (New!) ▸ Words that often appear near empty set ▸ Rhymes of empty set ▸ Invented words related to empty set