paterfamilias n.

Old English fæder "he who begets a child, nearest male ancestor;" also "any lineal male ancestor; the Supreme Being," and by late Old English, "one who exercises parental care over another," from Proto-Germanic *fader (source also of Old Saxon fadar, Old Frisian feder, Dutch vader, Old Norse faðir, Old High German fatar, German vater; in Gothic usually expressed by atta), from PIE *pəter- "father" (source also of Sanskrit pitar-, Greek pater, Latin pater, Old Persian pita, Old Irish athir "father"), presumably from baby-speak sound "pa." The ending formerly was regarded as an agent-noun affix.

My heart leaps up when I behold

  A rainbow in the sky:

So was it when my life began;

So is it now I am a man;

So be it when I shall grow old,

  Or let me die!

The Child is father of the Man;

I could wish my days to be

Bound each to each by natural piety.

[Wordsworth, 1802]

The classic example of Grimm's Law, where PIE "p-" becomes Germanic "f-." Spelling with -th- (15c.) reflects widespread phonetic shift in Middle English that turned -der to -ther in many words, perhaps reinforced in this case by Old Norse forms; spelling caught up to pronunciation in 1500s (compare mother (n.), weather (n.), hither, gather). As a title of various Church dignitaries from c. 1300; meaning "creator, inventor, author" is from mid-14c.; that of "anything that gives rise to something else" is from late 14c. As a respectful title for an older man, recorded from 1550s. Father-figure is from 1954. Fathers "leading men, elders" is from 1580s.

early 15c., "servants of a household," from Latin familia "family servants, domestics collectively, the servants in a household," thus also "members of a household, the estate, property; the household, including relatives and servants," abstract noun formed from famulus "servant, slave," which is of unknown origin.

The Latin word rarely appears in the sense "parents with their children," for which domus (see domestic (adj.)) was used. Derivatives of famulus include famula "serving woman, maid," famulanter "in the manner of a servant," famulitas "servitude," familiaris "of one's household, private," familiaricus "of household slaves," familiaritas "close friendship."

In English, sense of "collective body of persons who form one household under one head and one domestic government, including parents, children, and servants, and as sometimes used even lodgers or boarders" [Century Dictionary] is from 1540s. From 1660s as "parents with their children, whether they dwell together or not," also in a more general sense, "persons closely related by blood, including aunts, uncles, cousins;" earlier "those who descend from a common progenitor, a house, a lineage" (1580s). Hence, "any group of things classed as kindred based on common distinguishing characteristics" (1620s); as a scientific classification, between genus and order, from 1753.

Latin familia often was glossed in Old English by hired, hyred "household, family, retinue" (for which see hide (n.2), and also by hiwscipe, hiwræden, hiwan "members of a family, household,  or religious house," which is cognate with Old Norse hjon "one of the household; married couple, man and wife; domestic servant," and with Old High German hiwo "husband," hiwa "wife," also with Lithuanian šeimyna "family," Gothic haims "village," Old English ham "village, home" (see home (n.)). A 15c. glossary has, for Latin familia, Middle English a menge, from Anglo-French maisnie "the household, the whole attendance upon the personal establishment of the feudal lord."

As an adjective from c. 1600; with the meaning "suitable for a family," by 1807. Family values is recorded by 1966. Phrase in a family way "pregnant" is from 1796. Family circle is 1809; family man "man devoted to wife and children, man inclined to lead a domestic life" is 1856 (earlier it meant "thief," 1788, from family in a slang sense of "the fraternity of thieves"). Family tree "graph of ancestral relations" attested from 1752.

He was dressed in his best Coat, which had served him in the same Capacity before my Birth, and possibly, might be but little short in Antiquity, to the Root of his third Family Tree; and indeed, he made a venerable Figure in it. ["A Genuine Account of the Life and Transactions of Howell ap David Price, Gentleman of Wales," London, 1752]