The only free and comprehensive online etymological dictionary of the Spanish language
fámulo (Noun) "servant"

18th cent. From Latin famulus 'id.' From Proto-Italic *famelos "slave." From Proto-Indo-European *dhh1-m-elo- "foundation." From *dheh1- "to place." See also familia, hacer.

Romance: Western Vulgar Latin: Portugese fâmulo, Italian famulo

Indo-European: Hellenic: Ancient Greek θεμέλια (themélia) "foundation," θέμις (thmis) "justice"
fantasma m. (Noun) "ghost"

13th cent. Borrowed from Latin phantasma 'id.,' itself borrowed from Ancient Greek φάντασμα ‎(phántasma) 'id.,' from the verb φαίνειν (phaínein) "to make visible." From Proto-Indo-European *bh-n-eh2- 'id.' From *bheh2- "to shine."

Indo-European: Celtic: Old Irish bán "white;" Germanic: Norwegian bina "to stare," Middle High German büenen "to polish," Old English bōnian "to ornament;" Albanian: Gheg bâj "to make, Tosk bënj 'id.;' Armenian: banam "to reveal;" Indo-Iranian: Sanskrit bhā́ti "to shine," Avestan bānu- "splendor;" Tocharian: A pañi "splendor," B peñiyo 'id.'
fantástico (Adjective) "fantastic"

15th cent. Originally meaning "imaginary." Borrowed from Latin phantasticus "imaginary," itself borrowed from Ancient Greek φανταστικός ‎(phantastikós) "imaginary," but more literally "ghost-like." See fantasma for a continued etymology.

Romance: Western Vulgar Latin: Catalan fantàstic, Italian fantastico
favor m. (Noun) "favor"

15th cent. From Latin favor 'id.,' from favere "to favor," "to support." From favere "to favor." From Proto-Italic *faw-ē- 'id.' From Proto-Indo-European *bhh2u̯-eh1- "to be favorable to." From the root *bhh2u̯- "to become" (see fu-).

Romance: Western Vulgar Latin: Portugese favor, French faveur, Italian favore; Eastern Vulgar Latin: Romanian favoare

Indo-European: Celtic: Old Irish báe "profit;" Indo-Iranian: Sanskrit bhūṣ- "to exert"
favorecer (Verb) "to favor"

15th cent. From Vulgar Latin *favorescere 'id.' From Latin favor "favor" (see favor) with inchoative verb-forming suffix -escere (see -ecer).
faz f. (Noun) "face"

10th cent. According to Corominas (1991), the spelling of faz was archaic even in the 10th century. Faz was pronounced /(h)adz/. The modernist variant faz /fadz/ was introduced from Latin facies "face," "shape" in the 15th century. Of unknown origin.

Romance: Western Vulgar Latin: Portuguese face, Galician face, Catalan faç, French face, Italian faccia; Eastern Vulgar Latin: Aromanian fatsã, Romanian față; Sardinian: fache
fe f. (Noun) "faith"

12th cent. From Latin fides "trust." From Proto-Italic *fiþ-ē- 'id.' From Proto-Indo-European *bhidh-eh1- 'id.' From the verb *bhei̯dh- "to trust."

Romance: Western Vulgar Latin: Asturian fe, Portuguese , Galician fe, Catalan fe, French foi, Italian fede; Sardinian: fide

Italic: Umbrian fise (deity) "Trust"

Indo-European: Balto-Slavic: Old Church Slavonic běda "distress," Russian bedá "trouble," Czech bída "poverty," Bulgarian bedá "misery;" Albanian: "oath;" Hellenic: Ancient Greek πείθομαι (peíthomai) "to be convinced"

"Lat. fidēs preserves a very ancient meaning, blurred and simplified in other languages where the root *bheidh is represented, and altered even in Latin itself after a certain period; its meaning was not “trust” but “the inherent quality of a person which inspired confidence in him and is exercised in the form of a protective authority over those who entrust themselves to him.”" ~ E. Benveniste, Indo-European Language and Society (1973)
feliz (Adjective) "happy"

13th cent. From Latin felicem, accusative of felix "happy," but earlier "fruitful." From Proto-Italic *fēlwī-, which de Vaan (2014) evincingly interprets as "with young." From Proto-Indo-European *dheh1-lu̯-i- 'id.,' a hypercorrection of earlier *dheh1-lu̯- 'id.' From the noun *dheh1-l- "young animal." From the root *dheh1- "to suckle."

As there were myriad Catholic saints named Felix, myriad names and surnames appeared throughout Spain in Christian reverence: Feliz, Félez, Felices, Felies, Felis, San Félix, Félix, San Félix, Santelices, Sanfelis, and Sanfiz.

Romance: Western Vulgar Latin: Asturian feliz, Portuguese feliz, Galician feliz, Catalan feliç, Italian felice; Eastern Vulgar Latin: Romanian ferice

Indo-European: Celtic: Middle Irish deil "sow;" Germanic: Old High German tila "nipple," Old English delu 'id.;' Balto-Slavic: Lithuanian dėlė̃ "leech," Latvian dēle 'id.;' Hellenic: Ancient Greek θῆλυς (thêlus) "female;" Armenian: dayl "beestings;" Indo-Iranian: Sanskrit dhārú- "suckling"
-fero, -fer- Suffix "bring"

From Latin ferre "to bring." From Proto-Italic *fer-e/o- "to carry." From Proto-Indo-European *bher-e/o- 'id.'
ferro- Prefix "iron"

Very late 16th cent. From Latin ferrum 'id.' Of unknown origin. Possibly from Phoenician barzel "iron."

"The vocabulary associated with metallurgy is very restricted and at best we can attest the existence of copper/bronze, gold, and silver; words associated with later technologies such as 'iron' escape reconstruction to any great antiquity." ~ Mallory & Adams, The Oxford Introduction to Proto-Indo-European and the Proto-Indo-European World (2006)