Question

Etymologies are not very helpful in providing a definition of a word because

Answer 1

They are not very helpful because the meanings of words change over time.

This happen due to the combination of slangs and the unique application of the words based on various circumstances.
Due to this nature, the only thing that we can rely on to interpret certain words is the collective understanding that held by the social group when using the words.

Answer 2

Etymologies, it is the study of how the particular words are originated and the change in the meaning of the word along the history. Hence Etymologies are not a very helpful case because the meaning of the words may change with time and then on they are useful at all.