The word "gedda" is spelled as /ˈɡɛdə/ in IPA phonetic transcription. The "g" is pronounced as a hard "g" sound, as in "goat." The "e" is pronounced as the "e" in "bed." The "dd" is pronounced as a voiced "d" sound, followed by a slight pause, and then another voiced "d" sound. Finally, the "a" at the end is pronounced as the "a" in "about." The spelling of "gedda" accurately captures the pronunciation of this word in English.
The word "gedda" does not have a well-established etymology as it is not a widely recognized English term. However, if you are referring to "Jedda", it is derived from the Arabic word "Jiddah" (جدة), which means "grandmother" in English. "Jiddah" is also the name of a city in Saudi Arabia, which is highly probable to be the origin of the name.