"MW creu cannot be from *krū- (we would expect MW *kri, cf. ki < *kū 'dog'), but it may be from *kruwo-, a thematicized form, generalized from the oblique stem of the PCelt. root-noun (cf. PIE Gen. sg. *ḱruh₂-os)." (RM).
Matasović, Ranko. Etymological Dictionary of Proto-Celtic. Indo-European Etymological Dictionaries Online. Edited by Alexander Lubotsky. Brill. Brill Online: http://iedo.brillonline.nl.ludwig.lub.lu.se/dictionaries/content/proto-celtic/index.html
Robert Farren, PIE culture words collection, 2017
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