Being a native of Iceland I stumbled upon your page while searching for the waterfall Dynkur. Nice collection you have here! I could go on and on about waterfalls in Iceland but the original purpose of the comment was to give further insight into the name of Fardagafoss.
In Icelandic words are often concatinated together to form another word with a different meaning. This is the case for this name, so while you somewhat accurately translated each word the true meaning got lost in translation. “Far” can mean several related things but it stems from the verb “ferðast” which means to travel.
“Daga” is an inflected plural form of the noun “dagur” which simply means day but not dawn (which is “dögun”). So the meaning of “Fardaga” is literally “days of travel”.
Now I don’t know the particular history of this waterfall but in this context days of travel usually refers to the days of sheepherding in the fall but in a historical context it can also refer to trips from farms to towns and ports to access markets to buy and sell goods.
In any case it was a waterfall probably noticed mostly by local travelers during certain regular trips which is where the name comes from.
Love your detailed site and the trip reports! 🙂