Source : Webster's Revised Unabridged Dictionary (1913)

Sob \Sob\, v. i. [imp. & p. p. {Sobbed}; p. pr. & vb. n.
   {Sobbing}.] [OE. sobben; akin to AS. se['o]fian, si['o]fian,
   to complain, bewail, se['o]fung, si['o]fung, sobbing,
   lamentation; cf. OHG. s?ft["o]n, s?ft?n, to sigh, MHG.
   siuften, siufzen, G. seufzen, MHG. s?ft a sigh, properly, a
   drawing in of breath, from s?fen to drink, OHG. s?fan. Cf.
   {Sup}.]
   To sigh with a sudden heaving of the breast, or with a kind
   of convulsive motion; to sigh with tears, and with a
   convulsive drawing in of the breath.

         Sobbing is the same thing [as sighing], stronger.
                                                  --Bacon.

         She sighed, she sobbed, and, furious with despair. She
         rent her garments, and she tore her hair. --Dryden.

Source : WordNet®

sob
     v : weep convulsively; "He was sobbing inconsolably"
     [also: {sobbing}, {sobbed}]

sobbed
     See {sob}