This is simply "Dwarf", the singular form of Khazâd "Dwarves". Tolkien provides this singular/plural pairing as an example of Arabic-style broken plural patterns.
Khuzd would be "Dwarf" and singular, nominative, indefinite.
The Lord of the Rings: A Reader's Companion, pg 269
Parma Eldalamberon XVII: Words, Phrases and Passages, pg 35, 85