Here is an explanation of the word kawa'ib, as derived from its Arabic root, ka'b
Muhammad Asad has said regarding the above verse:
As regards my rendering of kawa’ib as "splendid companions", it is to be remembered that the term ka'b -from which the participle ka’ib is derived - has many meanings, and that one of these meanings is "prominence", "eminence" or "glory" (Lisan al-Arab); thus, the verb ka'ba, when applied to a person, signifies "he made [another person] prominent", "glorious" or "splendid" (ibid.) Based on this tropical meaning of both the verb ka'ba and the noun ka'b, the participle ka'ib has often been used, in popular parlance, to denote "a girl whose breasts are becoming prominent" or "are budding" hence, many commentators see in it an allusion to some sort of youthful "female companions' who would entertain the (presumably male) inmates of paradise.[2]
Then he continues:
...this interpretation of kawa’ib overlooks the purely derivative origin of the above popular usage - which is based on the tropical connotation of "prominence" inherent in the noun ka'b - and substitutes for this obvious tropism the literal meaning of something that is physically prominent: and this, in my opinion, is utterly unjustified. If we bear in mind that the Qur'anic descriptions of the blessings of paradise are always allegorical, we realize that in the above context the term kawa’ib can have no other meaning than "glorious [or "splendid"] beings".[2]