deriv LSK ETT STT aSTA ALPH OLDHOMEPAGE NEWHOMEPAGE
The "basic noun endings" (basic /sup) are those that appear in the list svaujasamauTch..., such as /su and /bhis.
The other noun endings are made by rules that replace them with something else.
As for instance, rule atobhisa::ais turns /bhis into /ais after most of the nounbases that end in a अ —
**azva- अश्वॱ m + /bhis
→ azva- अश्वॱ + ais ऐस् by atobhisa::ais
→ azvais अश्वैस् by vRddhireci
→ **azvais अश्वैस् "with horses"
This /bhis is a /sup ending because it appears in the svaujasamauTch... list, and the /ais is also a /sup ending because rule sthAnivadAd... says that whatever replaces a /sup is also a /sup.
Most nounbases get at least one ending replaced. AFAIK the base /nau- is the only one that gets all the basic endings unreplaced.
Many consonant bases, such as **vidyut- विद्युत्, keep all basic endings except /su, which is deleted by halGyAbbhyodIrgh....
The an अन्-enders like **rAjan- राजन् do the same thing, they get all the basic endings except /su, BUT the base itself changes its -an- into -An-, -a- or -n- sometimes (see endings after masculine an bases).
Unfortunately for students, the most common type of base, the masculines ending in a- अॱ like **azva- अश्वॱ, gets almost all of its endings replaced, or the a अ changed into something else, or both.