USECS from http://semanticwww.com
The largest lexical knowledgebase management system online.

USECS is a large lexical knowledgebase of English.
Nouns, verbs, adjectives and adverbs are grouped into ontological primitives,
each expressing a top level category of things.
All words are arranged in a common hierarchical network of entity names.
The resulting network of meaningfully related words and terms can be navigated with the browser.

USECS is available for download, in parts and as a whole content.
The structure of USECS makes it the most valuable means for building

ontologies
effective semantic web systems
inferential mechanisms
domain knowledge bases
advanced information retrieval systems
terminologies
vocabularies
natural language applications

USECS mottos:

Each name (URI) identifies a thing (a single Resource);
distinct names (URIs) are assigned to distinct things (Resources).

All names (URIs) make a single universal hierarchy of terms (identifiers),
used to uniquely identify any thing (Resource) in the world.