Dogs were animals in Middle-earth, similar to Foxes and Wolves, but domesticated.
The Races of Middle-earth had domesticated and employed dogs, with the notable exception of Dwarves who didn't have good relations with animals. Hobbits had domesticated dogs, like Farmer Maggot who owned three to guard his field.
Dogs bred for hunting were Hounds. The greatest of them all was Huan, the Hound of Valinor.
In Quenya, the word for "dog" is huo, and the Noldorin cognate of the same meaning is hû. Tolkien also experimented with other, onomatopoetic names: Quenya roa, grā, and wā(v).
In Gnomish, the early version of Noldorin, "dog" is also hû, and the additional cognate huil means "bitch". The word saur means "hound, wild dog".
Adûnaic also had its own terms for a dog, specifically raba in "common" gender singular ("dog", as a species/creature), the masculine singular rabô ("male dog"), the feminine singular rabê ("female dog", "bitch"), the plural rabî ("dogs"), and the dual (pair-plural) rabât ("a pair/duo of dogs"). There are also known declensed forms in the non-nominative cases, namely raban in the singular subjective case, rabīm in the plural subjective case, and rabu- in the objective case.   
Portrayal in adaptations
2007: The Lord of the Rings Online:
- Dogs are found throughout Middle-earth, especially in the Shire. Lore-masters can also have a non-combat dog pet.
- ↑ J.R.R. Tolkien, Christopher Tolkien (ed.), The Peoples of Middle-earth, "X. Of Dwarves and Men", "Relations of the Longbeard Dwarves and Men"
- ↑ J.R.R. Tolkien, Christopher Tolkien (ed.), The Peoples of Middle-earth, "X. Of Dwarves and Men", "Notes", n. 29
- ↑ J.R.R. Tolkien, Christopher Tolkien (ed.), The Lost Road and Other Writings, Part Three: "The Etymologies", p. 364-5 (root KHUGAN-)
- ↑ J.R.R. Tolkien, "Eldarin Hands, Fingers & Numerals and Related Writings — Part One" (edited by Patrick H. Wynne), in Vinyar Tengwar, Number 47, February 2005, pp. 35-6
- ↑ J.R.R. Tolkien, "I-Lam na-Ngoldathon: The Grammar and Lexicon of the Gnomish Tongue", in Parma Eldalamberon XI (edited by Christopher Gilson, Arden R. Smith, and Patrick H. Wynne), pp. 49, 67
- ↑ J.R.R. Tolkien, Christopher Tolkien (ed.), Sauron Defeated, "Part Three: The Drowning of Anadûnê, with the Third Version of The Fall of Númenor, and Lowdham's Report on the Adunaic Language", p. 434, 437
- ↑ Adûnaic - The Vernacular of Númenór, "Adûnaic Wordlist", Ardalambion (folk.uib.no) by Helge Fauskanger
- ↑ Adûnaic - "raba", "Adûnaic Words", Eldamo.org by Paul Strack