Dwarves are, by nature, a very private people.
Everyone else may think them unromantic, gruff, made of stone but “everyone else” is ultimately unimportant. When Dwarves love, they do so fiercely and passionately. And if that love is returned, then they feel no shame in showing their affection towards that loved one, from showering them with gifts to endearments.
Of course, Thorin Oakenshield is aware that most of his kith and kin tend to use treasure for their endearments. And there are many such words in Khuzdul. Thorin has found, to his great delight, that Khuzdul endearments, murmured in the prettily pointed ears (which were much more attractive than an Elf’s!) of a Certain Hobbit, tended to make said Hobbit shiver and blush most appealingly.
Bilbo is not a possession or a jewel or a pile of gold and mithril and while Thorin knows that his words mean that he values Bilbo far, far above these things, he feels that said endearments still fail to fully express his sentiments. So this is why that the endearments he tends to use the most often, even in his own tongue, mean love or beloved above all.
In Westron, Thorin finds himself simply calling Bilbo “beloved,” his tongue shaping the syllables as easily as if it were Bilbo’s name all along. It is only the truth, after all and if he often cannot help but nuzzle or kiss - preferably both - said Hobbit directly afterwards, then Bilbo needs to stop being so ridiculously adorable. Thorin is aware that is not going to happen and he is infinitely thankful to Mahal for this blessing.
There is, of course, one silly Khuzdul endearment that Thorin still calls Bilbo that is oddly suitable and has nothing to do with treasure whatsoever and has everything to do with the way that Bilbo reminds Thorin of tiny, adorable felines, especially when Bilbo puffs up in annoyance over something.
His sister-sons and the rest of his Company, especially certain Dwarven Warriors who happen to be cousins as well, are forbidden to ever tell Bilbo what that word means.
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