The affix khañ comes in the sense of 'what is travelled over or traversed in one day' after the word aśva being in the Genitive 6th-Case in construction.,
The word अश्वस्थ being in the sixth case shows the construction it should have before the affix. The एकाहगमः means एकाहेन गम्यते i.e. what is or can be gone over in one day. Thus अश्वस्यैकाहगमोऽध्वा = आश्वीनः, as आश्वीनानि शतं पतित्वा = यावन्ति योजनान्येकाहेनाश्वेन गम्यते तावतां शतं गत्वा ॥ सहस्राश्वीने वा इतः स्वर्गो लोकः ॥,