This is the 925th most frequent Czech word.
dostatečně
"Sufficiently" or "adequately."
The adverb 'dostatečně' is used here to describe the degree of robustness of the bridge, indicating 'enough'.
Tento most je dostatečně pevný, aby unesl nákladní auta.
This bridge is strong enough to bear trucks.
In this sentence, 'dostatečně' implies adequacy in the level of rest, describing in what measure the subject feels rested.
Cítíte se dostatečně odpočinutí po dovolené?
Do you feel rested enough after the vacation?
Here, 'dostatečně' modifies the adjective 'dlouho' to express the extent of time duration required.