father (n.) Look up father at Dictionary.com
Old English fæder "father, male ancestor," from Proto-Germanic *fader (cognates: Old Saxon fadar, Old Frisian feder, Dutch vader, Old Norse faðir, Old High German fater, German vater), from PIE *pəter (cognates: Sanskrit pitar-, Greek pater, Latin pater, Old Persian pita, Old Irish athir "father"), presumably from baby-speak sound like pa.
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; spelling caught up to pronunciation in 1500s (compare burden, murder, mother, weather). Father-figure is from 1954. Fathers "leading men, elders" is from 1580s.
father (v.) Look up father at Dictionary.com
c.1400, from father (n.). Related: Fathered; fathering.