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padre m. (Noun) "father"
12th cent. From Latin patrem, accusative of pater 'id.' From Proto-Italic *pater 'id.' From Proto-Indo-European *ph2tḗr "father," but more anciently "protector." From the root *peh2- "to protect."
Use in the plural meaning "parents" is from Vulgar Latin *patres "parents," "ancestors," "fathers;" accusative plural of Latin pater. The earliest Spanish texts when naming parents strictly use parientes. Only in the 13th cent. (and rarely) does padres "parents" occur. By the 14th cent., padres and parientes were in equal competition. Fahnestock & Peaks (1913) assume the Vulgar Latin use of *patres for both parents and fathers was under influence from Greek, which had done the same.

As a surname, given in religious reference to God the Father, second person of the Christian Trinity.
Variants
Chile, Andalucia, West Argentina paire. A hypocoristric development is Puerto Rico pay, Cuba pae, paíto.
Indo-European
Romance
Asturian , Portuguese pai, padre, Galician pai, padre, Catalan pare, French père, Italian padre, Romanian pater
Italic
Oscan patir "father," Venetic pater 'id.,' Marsian patre "to the father," South Picene patereíh 'id.'
Celtic
Gaulish atrebo "father," Old Irish athir 'id.'
Germanic
Gothic fadar "father," Old Norse faðir 'id.,' Old High German fatar 'id.,' Old Saxon fadar 'id.,' English father
Hellenic
Ancient Greek πατήρ (patér) "father," Mycenaean pa-te 'id.'
Armenian
Armenian hayr "father"
Indo-Iranian
Sanskrit pitár- "father," Old Avestan ptā 'id.'
Tocharian
A pācar "father," B pācer 'id.'

"Unlike [Late Proto-Indo-European] *māter ‘mother’, *pəter does not denote the physical parent, as is evidenced, for instance, by the ancient juxtaposition preserved in Latin Iupiter....

"The personal “father” is atta, which alone survives in Hittite, Gothic and Slavic. If in these languages the ancient term *pəter has been replaced by atta, this is because *pəter was originally a classificatory term." ~ E. Benveniste, Indo-European Language and Society (1973)