suff or sa-ow
(of the wind in trees, the sea, etc.) make a moaning, whistling, or rushing sound.
A word that probably warrants two separate entries as it can be pronounced in two totally different ways and can also be used as a noun [in singular] A moaning, whistling, or rushing sound as made by the wind in the trees or the sea.
“The wind soughed in the grass and there was the hiss of the tumbling river.”
“A sough escapes her lips as her body lands on the ground.”