Western etymological dictionaries trace the origin of the word 'God' to Old Frisian 'Du', which it is said had found its way into Old Frisian from Proto Germanic 'guthan' or 'gudan'. That is where the trail ends and 'guthan' therefore remains of unknown origin. In any case Proto-Germanic is a re-engineered language as are all languages which have the prefix 'Proto', and as such any claims made to etymology of words by 'Proto' languages obviously do not have cultural or scriptural literature to support them.

One may therefore turn to Sanskrit to help trace the etymology because it is the oldest language which has scriptures and literature that are understood to this day. One finds that the Old Frisian 'Du' is of Sanskrit origin and stems from 'deva' meaning 'deity' as do other European words for 'god' such as the French 'deu' and Greek 'theos'. The word 'deva' and its feminine form 'devi' appear in myriad ancient Vedic hymns and hence the contention made by sources such as 'wikipedia' that 'deva' and 'devi' appeared in Sanskrit from sources such as Latin or Persian are hugely erroneous for one will not find the origins of these words in Latin, Greek or Persian texts.

In fact, the etymology of 'guthan' and its many variations in European languages, are far better explained by Sanskrit rather than the later references made to them in texts in Europe or Central Asia. 'Guthan' has most likely originated from the Sanskrit 'huta' (हुत), which means 'that which is invoked', 'summoned', 'offered in sacrifice', or 'offered in fire'. The root word 'huta' appears in many forms in Sanskrit such as in the word 'ahuti' meaning 'sacrifice'. 'Huta' also appears repeatedly in Yajur Vedic verses and strotrams or hymns.

Most Hindi speakers are familiar with the word 'ahuti' (आहुति) which means 'invoking' or 'offering' both in Sanskrit and in Hindi, and, are derived from the root word 'huta' (हुत). In fact,  Zoroastrian 'ahura'  of 'Ahura Mazda' may also be derived from Sanskrit, taken to mean 'the invoker' or 'the one who is invoked'.

In the Vedic tradition 'huta' refers to Lord Indra. As an example here is a verse from the Sanskrit Sri Vishnu Sahsranama, a Strotram (hymn) from the ancient Hindu epic Mahabharata:

"Om ananta-huta-bhug-bhoktre-namah". Listen to the verse (with translation) here. The word appears in all its meanings in the verse mentioned above.

Some scholars trace the etymology of 'god' to PIE *ghu-to- "poured," from root *gheu- "to pour, pour a libation". First, the root word *gheu is linked to the Vedic 'ghee' which was the libation poured in a 'huta' (sacrificial fire). Second, the word 'ghee' itself, and the PIE *gheu are derivations of ancient Sanskrit 'ghrta' (घृत) which together appear in combination words such as 'ghRtAhuti' (घृताहुति); 'ghRtAhuti' contains the Sanskrit words for both- 'pouring ghee' and 'offering libations in the huta or sacrificial fire', thus establishing the link to the sacred fire offerings made to Vedic gods.

The source of Greek 'khein' meaning 'to pour' itself arises from the Sanskrit 'ghRtA' via 'ghee'. The Greek phrase 'khute gaia' meaning 'poured earth' which refers to reverence to burial mounds, also emerges from Sanskrit 'ghee'. Without the Vedic collateral of why 'pouring' is sacred, the Greek phrase 'khute gaia' does not convey the meaning.