Where to define a symbol that also has an abbreviation
If you actually have significant explanation beyond just expanding the abbreviation, I recommend putting that in the list of abbreviations and using a cross-reference from the list of symbols.  Just like an index can have &quot;attenuation coefficient, linear -- see linear attenuation coefficient&quot;, your lists of abbreviations and symbols could have, respectively,

LAC, linear attenuation coefficient, symbol \mu.  The linear attenuation coefficient applies to materials where absorbance dominates scattering as an attenuation mechanism, and total transmission energy follows Lambert's Law.
\mu, symbol for linear attenuation coefficient.  See also \hyperlink{LAC}

If there's no additional explanation, then both entries can be complete and short and a hyperlink would be pointless.

LAC, linear attenuation coefficient, symbol \mu
\mu, linear attenuation coefficient, abbreviated LAC