तेनैकदिक्

Operational rule vidhi

An affix -- प्राग्दीव्यतोऽण् (4.1.83) etc. comes after a word in the Instrumental -3rd case in construction in the sense of 'in the same direction with that'.

Word by word (padaccheda)

With / by तेन tṛtīyā · ekavacanaSubstitute / term एकदिक् prathamā · ekavacana

With / by Tṛtīyā (3rd case): accompaniment or means.
Substitute / term Prathamā (1st case): in operational rules, the substitute or the thing introduced; in definitions, the term or its referent.

Dotted words are technical terms. Hover or tap one to see its card.

Full reading

तेन एकदिक्

Pāṇini leaves out words that carry over from earlier sūtras. Expand to see the rule as a reader actually understands it.

Commentary

An affix -- प्राग्दीव्यतोऽण् 4.1.83 etc. comes after a word in the Instrumental -3rd case in construction in the sense of 'in the same direction with that'.
The word एक दिक means तुल्य दिक i.e. a common direction. Thus सुदाम्ना एकदिक = सौदामनी विद्युत् "a lightening, literally that which is in the same direction as the hill called the Sudaman." So हैमवती, त्त्रैककुदी, पैलुमूली ॥

The repetition of तेन, though it could have been supplied by anuvritti from 4.3.101, is for the sake of indicating that the anuvritti of the छन्दस् which regulated all the preceding ten sutras, does not extend to this aphorism, and therefore the तद्विषयता of 4.2.66 which was applied in those sutras does not apply here.

Śrīśa Chandra Vasu, The Ashtadhyayi of Panini (1897), via ashtadhyayi.com.