This is in the spirit of the What is a Word/Phrase™ series started by JLee with a special brand of Phrase™ and Word™ puzzles.
If a word conforms to a certain rule, I call it a Sound Word™.
Use the examples below to find the rule.
For those unable to view images, here is a text version of the table:
$$\begin{array}{|c|c|} \hline \text{Sound Words™}&\text{Not Sound Words™}\\ \hline \text{DECAY}&\text{DECOMPOSE}\\ \hline \text{QUEUE}&\text{LINE}\\ \hline \text{EIGHTY}&\text{FOURSCORE}\\ \hline \text{ENEMY}&\text{FOE}\\ \hline \text{EXPEDIENCY}&\text{EFFICIENCY}\\ \hline \text{ESCAPEE}&\text{FUGITIVE}\\ \hline \text{TEDIOUS}&\text{BORING}\\ \hline \text{DEVIOUS}&\text{TRICKY}\\ \hline \text{EXCELLENCY}&\text{EMINENCE}\\ \hline \text{IVY}&\text{VINE}\\ \hline \end{array} $$