According to Bing Translator 'kitten' (in English) translates as 'kitten' (In Klingon).
Not that Klingons would enjoy the company of a fluffy kitten; but this is the internet. Surely there must be a word for it?
Per the Klingon Wikia page for cat, the literal translation for kitten would be;
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Note that there's no direct translation of the word "cat" in the official Klingon language Dictionaries. In his Klingon for the Galactic Traveler, Mark Okrand (the creator of the Klingon Language) described the vIghro' as being a...
Type of animal, (like a cat) (n)
I kinda think there is no Klingon word for "kitten." Perhaps one way to approach this is to consider what the Universal Translator would do. We know that English speakers hear a Klington talk about his "targ." While Klingons treat targs very much like humans treat dogs--including eating them--the UT says "targ" not "dog."
I bet if you were telling a Klingon about how cute your adorable wittle kitty witty woockums was, he would probably hear the UT say "kitten" (and then he would kill you).
There are plenty of alien creatures that have Earth counterparts, in the which case they are referred to as such, e.g., Hupyrian beetle (in Ferengi snuff). But where there is no real similarity to Earth creatures, the UT will simply use the native word.
"Gagh" is a dish made from "serpent worm," so when a Klingon says "gagh" he is talking about food not worms. Like "steak" vs. "cow."
I'm just saying.