The only free and comprehensive online etymological dictionary of the Spanish language
paciente (Adjective, Noun) "patient"
15th cent. From Latin patientem, accusative of patiens 'id.' From pati "to experience" (see padecer), as a patient is one who experiences and endures a malady.
Indo-European
Romance
Portuguese paciente, French patient, Italian paziente, Romanian pacient
pacto m. (Noun) "pact"
13th cent. From Latin pactum "agreement," from the verb pascici "to form an agreement." From pax "peace" (see paz).
padecer (Verb) "to suffer;" "to endure"
13th cent. From Vulgar Latin padescere 'id.,' from pati "to experience" and an inchoative suffix -escere (see -ecer). Note that padecer replaced the more common Old Spanish verb padir "to suffer," taken free of the inchoative suffix from Vulgar Latin *padire 'id.,' from Latin *pati. From Proto-Italic *pat-i- 'id.' Of unknown origin. Theories include Proto-Indo-European *ph1-t- "suffering" and *pet-i- "to befall." Yet *ph1-t- would not yield pati in Latin and the primary sense of *pet- was "to fly," so the proverbial jury of specialists is still out.
Indo-European
Romance
Portuguese padecer, Catalan patir, French pâtir, Italian patire, Aromanian pat, pãtsãscu, Romanian păți, Sardinian patire
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)
pagar (Verb) "to pay"
12th cent. From Latin pacare, defined in Roberts (2014) as "to pacify (after having conquered)." A verb formed from pax "peace" (see paz).
Indo-European
Romance
Asturian pagar, Portuguese pagar, Galician pagar, Catalan pagar, French payer, Italian pacare, Romanian împăca, Sardinian pacare
Basque
Old Low Navarrese bakatu "pay," Roncalese pakatu 'id.,' both borrowed from Latin pacare; Bizkaian pagau "pay," borrowed from pagar
pago (1) m. (Noun) "farm;" "rural district"
Very late 15th cent. From Latin pagus 'id.,' literally "boundary marked by stakes." From Proto-Italic *pāg-o- "district," from Proto-Indo-European *peh2ǵ-os 'id.' From the root verb *peh2ǵ- "to attach."
Indo-European
Romance
Portuguese pago, French pays, Italian paese
Hellenic
Ancient Greek εὐ-πηγής (ey-pegés) "well-built"
Indo-Iranian
Sanskrit pajrá- "solid," Khotanese pāysa- "surface"
Pago (2) (Surname)
From Basque pago "beech," Medieval Basque bago. From Latin fagum 'id.' (see haya (1)).
país m. (Noun) "country"
Very late 16th cent. Borrowed from Old French pais "region," from Late Latin pagensis "one from the country," from Latin pagus "country." From Proto-Italic *pāg-o- "district." From Proto-Indo-European *peh2ǵ-o- "attachment." From *peh2ǵ- "to attach."
Indo-European
Romance
Portuguese país, French pays, Italian paese
Hellenic
Ancient Greek εὐ-πηγής (ey-pegés) "well-built"
Indo-Iranian
Sanskrit pajrá- "solid," Khotanese pāysa- "surface"
pájaro m. (Noun) "bird"
13th cent. Old Spanish passaro. From Vulgar Latin passar 'id.' Masculine ending -o (2) was added in Old Spanish due to hypercharacterization of its gender. Note also Appendix Probi (3rd or 4th cent.): passer non passar "[the word for bird is] passer, not passar." From Latin passer "sparrow". From Proto-Italic *pattro- 'id.' From Proto-Indo-European *pt-tro- "bird." From a root *pet- "to fly," with a possible (though tenuous) connection to pedir. This concise etymology is from Schrijver (1991), who proposes a reduction of the Proto-Italic nominative singular *pattros to a later *passr̥s and then finally passer.
Indo-European
Romance
Asturian páxaru, Portuguese pássaro, Galician paxaro, French passereau, Italian passero, Romanian pasăre
palabra f. (Noun) "word"
12th cent. Old Spanish parabla via metathesis. From Late Latin parabola "speech" but originally in Latin "comparison." Borrowed from Ancient Greek παραβολή (parabolé) "comparison;" "parable" (whence parábola).
Indo-European
Romance
Asturian pallabra, Portuguese parábola, Galician palabra, Catalan paraula, French palabre, Italian parabola, Romanian parabolă, Sardinian paragula