[Sigia-l] What is a "Top Term" in a thesaurus?

[Melvin Kumar]

Hello everyone,

I am trying to seek clarification of the meaning of the term "Top
Term" in a thesaurus.

I tried looking at the Z39.19 but it doesn't say anything about that.

I look at the thesaurus construction manual by  Aitchison, Jean, and
there is mention of term but no clarification of it.

Any theasurus experts out there can help me out?? 

Can point me to some book or website or give a description of the term
and its usage in the thesaurus. Would greatly appreciate your help.

Thank You in advance. 

Jay