छन्दोनाम्नि च

The word छन्द here means prosodial metre such as Gayatri & c; and not the Vedas; otherwise the word नाम would not have been used. Thus वि + स्तृ + घञ् = वि + स्तृ + घञ् 8.3.94 = विष्टारः 'the name of a metre called Vishtara-Pankti'.

The whole word विष्टारपङ्क्ति is the name of a metre, and is not a word ending with the affix ghan; only a member of this word, i.e. the first part ends with ghan. The seventh case-affix in the word छन्दोनाम्नि has the force of location i.e. when the word so formed occurs in a portion of a name of a metre; it is not the full name, but it is in the name i.e. forms a portion of the name.,