As a native Eng speaker "αρκετά" is one of my pet peeves. It can mean "much, many, a lot etc" but if we try to use it for "enough" we can get into linguistic trouble because "enough" means "as much as is needed". Therefore, αρκετά needs to be used with care. For some reason, "αρκετά" is often translated as "enough" causing unintelligible sentences.
Where the translation of "αρκετά" as "enough" began I cannot say but it has haunted me as an EFL teacher for over 50 years. There are indeed statements where it would be able to slip through but too many where it would not make sense.
"Enough" means "as much as is needed" or "sufficient" it does not mean simply "a lot, many, much etc".
Some recent examples of incorrect usage from students of English Ήταν αρκετά καταθλιπτικος.' would translate to "He was depressed enough." or "When the couple had argued enough they got a divorce." (Thus, "When the couple had argued as much as was needed they got a divorce." As if there were a fixed number of arguments.)
or "We had enough chairs for the dinner but some guests had to stand because they didn't have a chair." This is just plain incorrect. If there were as many chairs as are needed why did some guests have to stand because they didn't have a chair? You can see that in each case the student meant "a lot, many, a great deal etc" but "enough" doesn't fit at all.
So, please heed my explanation here and above and avoid using "αρκετά" unless you really mean to say "όσο χρειάζεται".
If, however, we are speaking about the Greek then "αρκετά and "πολή" are synonyms just don't confuse the English.
Oh, dear it's back. As you can see from my long-winded explanation above since there is no exact Greek translation for "enough" meaning "as much as is required" "αρκετά" is often used.
You might even find "αρκέτα" defined in dictionaries as "enough" which would be correct in some cases with context supporting it. So, your Greek friend was only repeating the prevailing notion. However, it would be remiss of us to encourage this general usage.
We do include "I am tired enough.'' as an accepted translation since without context we can't be sure.