caudex.

Uncertain. Most likely to be connected to cūdō (“to beat, strike”), both deriving from the same dental extension of Proto-Indo-European *kewh₂-, *keh₂w- (“to beat, hew, chop”), and so originally meant “that which has been cleaved off”. See also cauda (“tail”). Another possibility is a relation to caulis (“stalk”), if this is an l-stem derivative of the same ultimate root, perhaps *ḱawh₁- (“to swell; hollow”) (whence cavus) if both words originally meant “hollow stem”. An older idea connected it to Latin caupulus (“a kind of small boat”), based on the observation that similar words meaning “boat” and “tree” are often related in Indo-European languages, as many Indo-European peoples used hollowed out trees as boats and skiffs.