The root word for "sad" is likely the Old English word "sæd," meaning sated or full, which later evolved to mean "satisfied" and eventually "sorrowful" or "unhappy."
No dessert for me, thanks; I'm quite sated.
stuffed
sated
13th century: Old English saed 'sated, weary,' also 'weighty, dense,' of Germanic origin; related to Dutch zat and German satt, from an Indo-European root shared by Latin satis 'enough.' The original meaning was replaced in Middle English by the senses 'steadfast, firm' and 'serious, sober,' and later 'sorrowful.'
The close common word is satisfied (sated, content).
The word sated is in page two of The Call of the Wild.
The word 'spent' in this sense refers to being out of energy, or exhausted. 'Sated' refers to being satisfied. The phrase could be applied to someone who had just won a marathon or eaten at a very large buffet.
sated or satiated in English = saciado, in Spanish
Fugitive has no root word it is the root word.
empty
There is no root word of river. It itself is a root word.