I submit that the most beautiful word is 'beautiful'.

Such beauty lies in the mind of the beholder, musick.

For myself, I would say "birth" or "laughter" or "sunset" because of memories which I associate with these particular words.

Beautiful is what these things are, but they are not "beautiful" [at least "the most beautiful"] apart from my experience of them.

It occurs to me that the words we choose as "the most beautiful" are a mirror into our very soul.

Those who feel imprisoned will see more beauty in "liberty" than those who are free.

Those who are overcome with stress will see more beauty in "tranquility" than those who are overcome with boredom.

This is precisely the genius of the famous "Luscher Color Test". The primary color or colors a person chooses in preference to others is deeply revealing of that person's psychological state, even their state of health ... and these preferences will vary over time as these "states" vary in any given individual.