A soft and whispering sound, a murmur.
This wonderfuly calming noun stems from the reduplication of the Proto indo European root of swer. Swer, in turn, comes from the Sanskrit svarati, meaning sound and resound. But look how this one traveled the world- Greek syrinx means a flute while Latin surdus means mute or dull, Old Slavonic svirati means to whistle while Germanic schwirren is to buzz. Looks (or sounds) as if each and every culture who met this noun attested it to a certain sound.
Why this word?
I am a huge fan of onomatopoeia, to me, this phenomena is the bridge between this obscure creature called language, and humanity.
This word sounds exactly as what it stands for. Try it out; say it. You can even repeat it, it would not take too long until you would actually be able to imagine yourself on a hammock, on a deserted island at the shores of Thailand, sipping margarita and listening to the silent susurration of the waves and leaves…
How to use this susurrus?
Use it to describe these sounds; out at nature, in the forest, at the beach, wherever the wind lightly blows and gently caresses anything in its way.