I’m probably missing something - but why not go for the more obvious sandhi of eka+udi ?
The PTS dictionary even refers to ekodi, and a sense of one-arising would fit well with the 2nd jhana
udi
(or udī) is artificial adj. formn. fr. udeti, meaning “rising, excelling”, in expln. of ekodi at Vism.156 (udayatī ti udi uṭṭhapetī ti attho).