sigh          
 verb [ I ] uk/saɪ/ us/saɪ/
B2 叹息,叹气
to breathe out slowly and noisily, expressing tiredness, sadness, pleasure, etc.
  She sighed deeply and sat down. 她深叹一口气,坐了下来。 
 [ + speech ] "I wish he was here," she sighed (= she said with a sigh). “我希望他在这里,”她叹息道。 
  (风穿过树林时)发出呜咽声
If the wind sighs, it makes a long, soft sound as it moves through trees.
  I lay on my back, listening to the sound of the wind sighing in the trees. 我仰面躺着,听着风穿过树林发出的呜咽声。 
 - More examples
 - He sighed heavily and returned to his book.
 - 'I'll never understand these instructions,' he sighed.
 - When I suggested a walk, she simply sighed.
 - He sighed in despair as he read the letter.
 
sigh       
noun [ C ] uk/saɪ/ us/saɪ/
B2 叹息,叹气
a slow, noisy breath
  He leaned back in his seat with a sigh. 他向后靠在座位上长出了一口气。 
 "Ah, you're here," she said and heaved/let out/gave a sigh of relief. “啊,你在这儿,”她说道,如释重负地松了口气。