weather (n.)

Middle English fader, from 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).

This is from the PIE root *pəter- "father" (source also of Sanskrit pitar-, Greek pater, Latin pater, Old Persian pita, Old Irish athir "father"), which is presumably from baby-speak sound "pa." The ending formerly was regarded as an agent-noun affix. The classic example of Grimm's Law, where PIE "p-" becomes Germanic "f-."

The spelling with -th- (15c.) reflects a widespread phonetic shift in Middle English that turned -der to -ther in many words, perhaps reinforced in this case by Old Norse forms; the spelling caught up to pronunciation in 1500s (compare mother (n.), weather (n.), hither, gather).

As a title of various Church dignitaries from c. 1300; the 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.

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]

Middle English le, leoh, from Old English hleo "shelter, cover, defense, protection," from Proto-Germanic *khlewaz (source also of Old Norse hle, Danish læ, Old Saxon hleo, Dutch lij "lee, shelter"). The original sense is uncertain; it might have been "warm" (compare German lau "tepid," Old Norse hly "shelter, warmth"), and Watkins traces it to a PIE *kle-wo-, a suffixed variant form of the root *kele- (1) "warm."

Nautical sense "that part of the hemisphere to which the wind is directed" (c. 1400) is of Scandinavian origin, from the notion of the side of the ship opposite that which receives the wind as the sheltered side. As an adjective, 1510s, from the noun. The lee shore is that toward which the wind blows. Middle English also had lewth "warmth, shelter," Old English hleowþ, with Proto-Germanic abstract noun suffix *-itho (see -th (2)). Also compare lukewarm.