Aisa (Ais)

Thill, shaft or harness-pole of a draught vehicle. Road now buried beneath a car park servicing the Rocca al Mare ice rink and tennis courts, with a remaining 27.4 m of dirt track facilitating travel to a nearby spruce. A tantalizing word probably loaned from one of 2 much studied PIE roots, these being:

from Proto-Baltic *ajesa, itself from PIE *ei- or *oi- giving Sanskrit ईषा (īṣā́: shaft, board, plank), Hittite 𒄭𒅖𒊭𒀭 (ḫi-iš-ša-an: tiller), Anc. Gk, οἴηξ (oíēx: shaft, tiller), Eng. oar, (>Old Eng. ār-), ON þilja (thilja: board or plank) and Ru. воз (vojë: shaft or cart), from Old Slavonic *vozъ itself from Proto-Slavic *oje(s) (tiller),
but…
perhaps too from another PIE term designating an axle, *ak*s, as in Sanskrit अक्ष (áks*a), axis, Old Prussian assis, Lith. ašís, etc.

Other sources suggest ais is to be a loan word from old Pskov and Novgorod Russian, but which?... The point here is that given the multiple forking of the ‘original’ PIE meaning into new usages, coupled with probable metonymy (e.g. saying ‘wheels’ or ‘motor’ instead of ‘car’), it is possible that the flatness of the former and pole-ness of the latter merged into one and was absorbed into Estonian, but don’t quote me on it…