A kitten is a juvenile

Juvenile (organism)

A juvenile is an individual organism that has not yet reached its adult form, sexual maturity or size. Juveniles sometimes look very different from the adult form, particularly in terms of their colour...

 domesticated

Domestication

Domestication or taming is the process whereby a population of animals or plants, through a process of selection, becomes accustomed to human provision and control. In the Convention on Biological Diversity a domesticated species is defined as a 'species in which the evolutionary process has been...

 cat

Cat

The cat , also known as the domestic cat or housecat to distinguish it from other felids and felines, is a small, usually furry, domesticated, carnivorous mammal that is valued by humans for its companionship and for its ability to hunt vermin and household pests...

.

The young of big cat

Big cat

The term big cat – which is not a biological classification – is used informally to distinguish the larger felid species from smaller ones. One definition of "big cat" includes the four members of the genus Panthera: the tiger, lion, jaguar, and leopard. Members of this genus are the only cats able...

s are called cub

Cub

A cub is the young of certain large predatory animals such as bears, lions, wolves, and big cats; analogous to a domestic puppy or kittenCub may refer to:* Cub, a member of Cub Scouts* Cub player, a member of certain sports teams, e.g...

s rather than kittens. Either term may be used for the young of smaller wild felids

Felidae

Felidae is the biological family of the cats; a member of this family is called a felid. Felids are the strictest carnivores of the thirteen terrestrial families in the order Carnivora, although the three families of marine mammals comprising the superfamily pinnipedia are as carnivorous as the...

 such as ocelot

Ocelot

The ocelot , pronounced /ˈɒsəˌlɒt/, also known as the dwarf leopard or McKenney's wildcat is a wild cat distributed over South and Central America and Mexico, but has been reported as far north as Texas and in Trinidad, in the Caribbean...

s, caracal

Caracal

The caracal is a fiercely territorial medium-sized cat ranging over Western Asia, South Asia and Africa.The word caracal comes from the Turkish word "karakulak", meaning "black ear". In North India and Pakistan, the caracal is locally known as syahgosh or shyahgosh, which is a Persian term...

s, and lynx

Lynx

A lynx is any of the four Lynx genus species of medium-sized wildcats. The name "lynx" originated in Middle English via Latin from Greek word "λύγξ", derived from the Indo-European root "*leuk-", meaning "light, brightness", in reference to the luminescence of its reflective eyes...

, but "kitten" is usually more common for these species.
The word "kitten" derives from Middle English

Middle English

Middle English is the stage in the history of the English language during the High and Late Middle Ages, or roughly during the four centuries between the late 11th and the late 15th century....

 kitoun (ketoun, kyton etc.), which itself came from Old French

Old French

Old French was the Romance dialect continuum spoken in territories that span roughly the northern half of modern France and parts of modern Belgium and Switzerland from the 9th century to the 14th century...

 chitoun, cheton: "kitten".
A feline litter

Litter (animal)

A litter is the offspring at one birth of animals from the same mother and usually from one set of parents. The word is most often used for the offspring of mammals, but can be used for any animal that gives birth to multiple young. In comparison, a group of eggs and the offspring that hatch from...

 usually consists of two to five kittens.