sth like "you are really sth" "oh no""can't believe it"

v. intr.
To exhale audibly in a long deep breath, as in weariness or relief.
To emit a similar sound: willows sighing in the wind.
To feel longing or grief; yearn: sighing for their lost youth.

v. tr.
To express with or as if with an audible exhalation.
Archaic To lament.

n. The act or sound of sighing.