Definition: indeclinable, lit. invariant, not undergoing a change. Pāṇini has used the word as a technical term and includes in it all such words as स्वर्, अन्तर्, प्रातर् etc, or composite expressions like अव्ययीभावसमास, or such taddhitānta words as do not take all case affixes as also kṛdanta words ending in म् or ए, ऐ, ओ, औ. He gives such words in a long list of Sutras P. I.1.37 to 41; cf. सदृशं त्रिषु लिङ्गेषु सर्वासु च विभक्तिषु । वचनेषु च सर्वेषु यन्न व्येति तदव्ययम् Kāś. on P.I.1.37.