Short answers, pulled from the story.
The English word god descends from Old English god, which comes from the Proto-Germanic word gudą. Cognates of gudą survive in Gothic, Old Norse, Old Saxon, Old Frisian, Old Dutch, and Old High German.
Scholars disagree on the original meaning of the Proto-Germanic gudą. One theory ties it to pouring, meaning a libation or an idol, or, per Watkins, the spirit inhabiting a burial mound, while a second theory ties it to invoking, meaning an invocation, a prayer, or that which is invoked.
Bishop Ulfilas is often credited with the earliest written use, in his fourth-century Gothic translation of the Bible, sometimes called the Wulfila Bible. He translated the Bible into Gothic in Nicopolis ad Istrum, in what is now northern Bulgaria, using the words guda and guþ for God.
Theos, the Greek word for god, is often connected to θέω, meaning to run, and θεωρέω, meaning to look at, to see, or to observe, as well as Latin feriae and fanum. An alternative theory credited to De Saussure ties theos to the root dhu̯es-, meaning smoke or spirit, related to Latin fumus, meaning smoke.
God and its cognates started as grammatically neuter nouns in a language that still sorted nouns by gender. Conversion to Christianity pushed the word toward the masculine, though traces of the old neuter grammar survive in the Gothic phrase guþ meins, meaning my god, where guþ still lacks the final -s of a masculine noun.
Capitalized God first referred specifically to the Abrahamic deity, a convention that grew out of Christian texts shaping English spelling. It is not used for multiple gods or the generic idea of a deity, though it now also covers monotheistic terms such as the Arabic Allāh, the Persian Khuda, the Indic Ishvara, and the Maasai Ngai.