And the words ending in taddhita or secondary affixes -- taddhitāḥ [[4.1.76]], which are not declined in all the cases are also avyaya or indeclinables.,
This expands the definition of avyaya. There are three words in the sutra taddhitah, cha and asarva-vibhaktih. Taddhitas or secondary affixes are certain affixes, by which nouns are derived from other nouns, such as, from मनु we have मानवः, sarva-vibhaktis are those words which take all case-terminations, asarva-vibhaktis are those which do not take all vibhaktis but some only. Thus the adverb यतः is declined in the singular ablative only, and does not take the dual and plural terminations.
Those derivative words which do not take all the case-terminations, but only some of them and which are formed by the addition of Taddhita affixes are indeclinables. As ततः 'thence,' तत्र 'there.' Both these words are formed by taddhita affixes from the pronoun तद् 'that,' the one is used in the ablative case only and the other in the locative. So also यतः, यत्र, तदा, यदा, सर्वदा &c.,