The Labyrinth (updated)

Greek labýrinthos (Mycenean DA-PU-RI₂-TO-JO 'of the labyrinth') designated an elaborated place built by the artificer Daedalus for the king Minos of Crete and whose function was to hold the Minotaur, a legendary creature half man and half bull. Although the Cretan labyrinth had a square or rectangular shape, there is an older circular version found in several ancient cultures, mostly in petroglyphs. 

From the Greek word, I'd reconstruct Minoan¹ *ɮabur 'fence, wall', with an initial voiced lateral represented as /d/ in Linear B. Seemingly related words are Central Chadic *ɮabˁ- 'fence, to fence', Low East Cushitic (Afar) sabsab- 'wall' (reduplicative), Egyptian ʃzp(a) 'fence',  Etruscan spur 'city'. 

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¹ The Pre-Greek language spoken at Crete, attested in Linear A tablets and loanwords to Greek.

Celtic *longā 'boat, vessel' (updated)

Celtic *longā 'boat, vessel' is attested in Welsh llong 'ship', Old Breton locou 'vessels, vases', Old Irish long 'vessel, (little) vase, ship', to which corresponds the Gaulish toponymic element Longo-¹. There's also Cisalpine Gaulish (Todi) lokan /longan/ 'cinerary urn', an accusative form where /ng/ is rendered as k.

Although some authors have suggested a loanword (with reanalysis) from Latin nauis longa 'warship' (lit. 'long ship'), specialists such as Matasović² think this is a genuine Celtic word without IE etymology, which I consider it to be a cultural loanword from North East Caucasian *leqˀV 'a k. of vessel' (NCED 1511), where the ejective stop became prenasalized. Also related would be Latin lanx 'dish, plate'³, apprently borrowed from Etruscan in account of its /a/ vocalism.

This lexeme was also borrowed into IE *lonko-/ā 'valley' > Lithuanian lankà ‘valley, rivermeadow’, Old Church Slavonic lǫka ‘gulf, valley, meadow, marsh’, Tocharian B leṅke ‘valley’, and Late Latin *lanca ‘depression, bed of a river’⁴, with a straightforward semantic shift.

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¹ X. Delamarre (2008): Dictionnaire de la langue gauloise, p. 206-207.

² R. Matasović (2009): Etymological Dictionary of Proto-Celtic, p. 244.

³ This meaning is reflected in Tsezian.

⁴ J.P. Mallory & D.Q. Adams (2006): The Oxford Introduction to Proto-Indo-European and the Proto-Indo-European World. 122.