Source : Webster's Revised Unabridged Dictionary (1913)

Sigh \Sigh\, n. [OE. sigh; cf. OE. sik. See {Sigh}, v. i.]
   1. A deep and prolonged audible inspiration or respiration of
      air, as when fatigued or grieved; the act of sighing.

            I could drive the boat with my sighs. --Shak.

   2. Figuratively, a manifestation of grief; a lan?ent.

            With their sighs the air Frequenting, sent from
            hearts contrite.                      --Milton.

Sigh \Sigh\, v. i. [imp. & p. p. {Sighed}; p. pr. & vb. n.
   {Sighing}.] [OE. sighen, si?en; cf. also OE. siken, AS.
   s[=i]can, and OE. sighten, si?ten, sichten, AS. siccettan;
   all, perhaps, of imitative origin.]
   1. To inhale a larger quantity of air than usual, and
      immediately expel it; to make a deep single audible
      respiration, especially as the result or involuntary
      expression of fatigue, exhaustion, grief, sorrow, or the
      like.

   2. Hence, to lament; to grieve.

            He sighed deeply in his spirit.       --Mark viii.
                                                  12.

   3. To make a sound like sighing.

            And the coming wind did roar more loud, And the
            sails did sigh like sedge.            --Coleridge.

            The winter winds are wearily sighing. --Tennyson.

   Note: An extraordinary pronunciation of this word as s[=i]th
         is still heard in England and among the illiterate in
         the United States.

Sigh \Sigh\, v. t.
   1. To exhale (the breath) in sighs.

            Never man sighed truer breath.        --Shak.

   2. To utter sighs over; to lament or mourn over.

            Ages to come, and men unborn, Shall bless her name,
            and sigh her fate.                    --Pior.

   3. To express by sighs; to utter in or with sighs.

            They . . . sighed forth proverbs.     --Shak.

            The gentle swain . . . sighs back her grief.
                                                  --Hoole.

Source : WordNet®

sigh
     n 1: an utterance made by exhaling audibly [syn: {suspiration}]
     2: a sound like a person sighing; "she heard the sigh of the
        wind in the trees"

sigh
     v 1: heave or utter a sigh; breathe deeply and heavily; "She
          sighed sadly" [syn: {suspire}]
     2: utter with a sigh