स्वरादिनिपातमव्ययम्

The words स्वर् 'heaven' etc. and the particles -- निपात एकाजनाङ् 1.4.56, are called अव्यय or indeclinables.
This defines avyaya or indeclinables. The words स्वर् &c. must be found out from the Ganapatha; they are the following:--

स्वर् 'heaven,' अन्तर् 'midst,' प्रातर् 'in the morning,' पुनर् 'again,' सनुतर् 'in concealment,' उच्चैस् 'high, aloft' नीचैस् 'low down,' शनैस् 'slowly,' ऋधक् 'rightly, separately, aside, singly, particularly, truly,' ऋते 'except, without,' युगपत् 'at the same time, at once,' आरात् 'near, far from, directly.' पृथक् 'separately, apart,' ह्यस् 'yesterday,' श्वस् 'to-morrow,' दिवा 'by day,' रात्रौ 'by night or in the night,' सायम् 'at eve,' चिरम् 'long, long since, a long time,' मनाक् 'a little,' ईषत् 'slightly, a little,' शश्वत् 'ever,' जोषम् 'gladly,' तूष्णीम् 'silently,' बहिस् 'outside,' अविस् 'below, without, outside.' समया 'near,' निकषा 'near, hard, close by,' स्वयम् 'of one's self,' वृथा 'in vain,' नक्तम् 'at night, by night,' नञ् 'negative particle, not,' हेतौ 'for this reason, by reason of,' इद्धा 'truly, really' हे ह 'exclamation,' अद्धा 'evidently, truly,' सामि 'half,' वत बत 'enclitic like, as Brahmanavat, priestly,' सनत् सनात् 'perpetually,' उपधा 'division,' तिरस् 'crookedly, awry, over,' अन्तरा, अन्तरेण 'except, without' ज्योक, योक 'long,' कम् 'expletive particle,' शम् 'ease,' सना 'perpetually,' सहसा 'suddenly, hastily,' विना 'without,' नाना 'variously,' स्वस्ति 'greeting, peace,' स्वधा 'exclamation, oblation to Manes,' अलम् 'enough,' वषट् 'exclamation,' श्रौषट्, वौषट् (interjection) 'oblation of butter,' अन्यत् 'again, moreover, otherwise.' अस्ति 'being present,' उपांशु 'in a low voice, secretly, privately,' क्षमा 'patience, pardon,' विहायसा 'aloft in the air,' दोषा 'at night or in the evening,' मृषा, मिथ्या 'falsely,' मुधा 'in vain,' पुरा 'formerly,' मिथो or मिथस् 'mutually, together,' प्रायस् 'frequently, almost,' मुहुस् 'again, repeatedly' उवाहकम् or उवाहिका 'at the same time,' आर्यहलम् 'violently' अभीक्ष्णम् 'repeatedly,' साकम् or सार्धम् 'with' नमस्, 'reverence,' हिरुक् 'without,' धिक् 'fie!' अथ 'thus,' प्रताम् 'with fatigue,' प्रशान् 'alike,' प्रतान् 'widely,' मा, माङ 'do not.'

So, also the words formed by the affixes ktva tosun, kasun, by the krit affixes ending in म् or ए, ऐ, ओ or औ, and the avyayibhava compounds, are indeclinables. So, also the words formed by the affixes beginning with तसिल् 5.3.7 and ending with पाशप् 5.3.47, by the affixes beginning with शस् (V. 4.4.2) and ending with समासांतः 5.4.68, by the affixes कृत्वसुच्, सुच्, आच् and थाल् by the affixes having the sense of the affix च्वि, or by the affixes अम् or आम्, तसि or वति, न or नाञ् are also indeclinables.

The words called nipata will be given under sutras, 1.4.56 to 1.4.61. Thus a word which changes not (न व्येति), remaining alike in the three genders and in all cases, and in all numbers, is what is termed an अव्यय or indeclinables.