The Basque word for 'nest' appears with variants such as abia (B), habia (Z), kabia (G), kafia (G, HN), abira (S), abi (B), kabi (G, HN), api (G, HN), aapi (G). For this word, Mitxelena -the founder of modern Vascology- proposed more than 50 years ago an etymology from Latin cavea 'cage', which turns to be semantically inadequate.
By contrast, I propose a loanword from Celtic *āwjā 'brood; nest', a femenine form corresponding to the masculine *āwjo- 'egg' (Old Welsh ui, Middle Welsh wy, Middle Breton and Old Cornish uy)1. Therefore, both k- and -r- in some of the Basque forms would be epentic.
On the other hand, the forms abe (B) 'honeycomb', kabe (*L) 'nest; beehive' are the result of a semantic contamination with derivatives of Romance *kofanu 'deep basket' (Latin cophinus) such as Biscayan abao, abau 'honeycomb' and Bearnese càben 'beehive'. The semantic drift can be explained because artificial beehives in the shape of a deep basket are used in some places.
1 R. Matasović (2008): Etymological Dictionary of Proto-Celtic, p. 50.