Weekly Georgian Etymology: ჩრდილოეთი črdiloeti ‘north’, lit. land of shadow, from Old Georgian ႹႰႣႨႪႭ črdilo shadow plus –et, < čero shadow poss from PIr *caHyáH + PK *dil- morning. In many west Eurasian lgs, words for north are commonly associated with darkness, shadow or night.

It is first attested in Leonti Mroveli’s 10th c account of the 1st c BC king Artoces: მისცა ქალაქი მცხეთა და… ყოველი ქართლი მტკუარსა ჩრდილოეთი ‘He gave the city of Mtskheta and... all Kartli north of the Mtkvari [River]'

The word ჩრდილო črdilo itself probably originally meant not just any shadow but the darkness of morning twilight: it is transparently composed of ჩერო čero, also 'shade, shadow', and დილ- dil- 'morning'.

ჩერო čero itself seems to be an ancient loan from a very early Proto-Iranian lg, but which precise one is unclear. PIE *(s)ḱeh₃ih₂ shadow becomes Proto-Iranian *caHyáH regularly (after s-mobile is lost), but the problem is none of these lgs undergo rhotacism of the medial /y/.

Indic lgs DO sometimes undergo rhotacism in this precise environment: e.g. Sanskrit छाया čāyā becomes Bengali ছাইড়া čaiṛa. This is possibly because a separate suffix is involved: *chāyā-illa is the Ashokan Prakrit form. Whether something similar happened is unclear.

Be that as it may, Georgian ჩერო *čero is a very old loan whose origin has not been pinned down. It was compounded with დილა dila 'morning' already in Old Georgian to mean 'twilight darkness'.

So how did this word for darkness become associated with the cardinal direction of north? Across western Eurasian lgs, the metaphor of darkness is common:

Proto-Balto-Slavic: *śḗˀwer- dark, murky
Bashkir төньяҡ night-side
Hungarian észak night-piece
Polish północ midnight

This metaphor which stems from obvious facts about seasonal light and dark have very ancient associations specifically with the Pontic-Caspian steppe, as Homer describes this home of the Iranian-speaking Cimmerians thus:

This lexical pattern probably spread in the first millennium, as it is a widespread across lg families that only achieved their current geographical distribution after around 300-800 AD, including Kartvelian, Slavic, Hungarian, Turkic and Balkan Romance lgs:

Other evidence for this fact is that it is not shared at deeper phylogenies. Hungarian has észak 'night-piece' for north, but Finnish has pohjoinen 'bottom-land'; Latin had septentriō 'land of Ursa Major', but Aromanian has njeadzã-noapti, from media noct- 'midnight'.

All of this suggests that Georgian must have borrowed this metaphor for the cardinal direction in late antiquity, during the middle of the first millennium AD.