Hello Mater: 8 Obscure Words for Family

The respective rights and claims of matrikin and patrikin are well exemplified in the arrangement of marriages.
— Meyer Fortes, Kinship and the Social Order, 1970

These words refer respectively to one's maternal and paternal relatives. The matr- and patr- parts are Latin, but the kin part is from English's earliest Germanic days. Kin originally referred to a group of people of common ancestry, but your kin are also the people who likely come to mind when you think of your relatives. This meaning is the word's most common one, and it's a meaning the word has had since the 9th century.

Other family words related to kin are kinfolk (and kinsfolk), kindred, kinship, and kinsman and kinswoman.

The adjective german (note the lower-case "g") means "having the same parents or the same grandparents on either the maternal or the paternal side." It's usually hitched onto a noun with a hyphen in terms like brother-german or cousin-german. The word also has a related noun german, now obsolete, meaning "a near relative."

… you'll have your nephews neigh to you; you'll have / coursers for cousins, and gennets [female donkeys] for germans.
— Shakespeare, Othello, 1622

This german comes from the Latin word germānus, "having the same parents," which likely traces back to gignere, meaning "to bring into being, to give birth to." Despite appearances, it's highly unlikely that the word has any relation to Germānī, a name that was used by Caesar for a group of tribes in northeastern Gaul and was modified and more broadly applied by later Roman writers.

As a noun, distaff most often refers to the female part or branch of a family. As an adjective, it describes those related through a mother—for example, your mother's side of the family.

They inherit Plantagenet blood by direct descent, and Tudor on the distaff side.
— Arthur Conan Doyle, The Adventures of Sherlock Holmes, 1892

The dis in distaff is not the negating or opposing dis- of disagree or disconnected. It actually has to do with flax. A distaff was originally a short staff used to hold a bundle of fibers—originally flax—ready to be spun into yarn or thread. Because of the close association of women with spinning, the distaff itself came to be a symbol of the work or domain of women.

Distaff is sometimes contrasted with spear, which functions as an adjective describing those related through a father.

A genetrix (plural: genetrices) is a mother, and especially a biological mother. The word comes from the Latin gignere, meaning "to beget," and is contrasted with genitor, which can refer to a father (especially a biological one) or, more generally, to a parent.

… anthropologists distinguish between the culturally defined "father" and the genitor, the actual biological father. A similar distinction is necessary in the case of "mother." Although the culturally defined mother is usually the genetrix, the widespread practice of adoption also creates many discrepancies….
— Marvin Harris, Culture, People, Nature, 1988

Filial is an adjective meaning "of, relating to, or befitting a son or daughter" or "having or assuming the relation of a child or offspring."

No human being could have passed a happier childhood than myself. My parents were possessed by the very spirit of kindness and indulgence. We felt that they were not the tyrants to rule our lot according to their caprice, but the agents and creators of all the many delights which we enjoyed. When I mingled with other families, I distinctly discerned how peculiarly fortunate my lot was, and gratitude assisted the development of filial love.
— Mary Shelley, Frankenstein, 1818

Filial comes from the Latin filius, meaning "son," but filial has for all of its more than 600 years in English has always had to do with both sons and daughters.

A kissing cousin isn't necessarily the son or daughter of your aunt or uncle. In fact, kissing cousin has a meaning completely removed from family and potentially even of animate beings: "one that is closely related in kind to something else." It also refers, in a nod to the literal meaning of its second element, to a person (especially a relative) you know well enough to kiss upon greeting.

Summer time was family time. Big time family time, a whole island of family, here a cousin, there a cousin, everywhere we turned a kissing cousin was puckering up at us.
— Julia Alvarez, How the Garcia Girls Lost Their Accents, 1991

Kissing cousin is a 20th century creation. The earliest currently available evidence of it in use is from 1941.

A parallel cousin, on the other hand, is indeed a literal cousin. The word refers specifically to "one of two cousins who are children of two brothers or two sisters." It's contrasted with cross-cousin, which means "one of two cousins especially of different sex who are respectively the children of a brother and sister."

Both terms are used mostly in anthropology:

Children whose parents are related to each other as brother and sister are known as cross cousins; children whose parents are related to each other as brother and brother or sister and sister are known as parallel cousins.
— Marvin Harris, Culture, People, Nature, 1988