Source : Webster's Revised Unabridged Dictionary (1913)

Undulate \Un"du*late\, v. i.
   To move in, or have, undulations or waves; to vibrate; to
   wave; as, undulating air.

Undulate \Un"du*late\, a. [L. undulatus undulated, wavy, a dim.
   from unda a wave; cf. AS. ??, Icel. unnr; perhaps akin to E.
   water. Cf. {Abound}, {Inundate}, {Redound}, {Surround}.]
   Same as {Undulated}.

Undulate \Un"du*late\, v. t. [imp. & p. p. {Undulated}; p. pr. &
   vb. n. {Undulating}.]
   To cause to move backward and forward, or up and down, in
   undulations or waves; to cause to vibrate.

         Breath vocalized, that is, vibrated and undulated.
                                                  --Holder.

Source : WordNet®

undulate
     adj : having a sinuate margin and rippled surface
     v 1: stir up (water) so as to form ripples [syn: {ripple}, {ruffle},
           {riffle}, {cockle}]
     2: occur in soft rounded shapes; "The hills rolled past" [syn:
        {roll}]
     3: move in a wavy pattern or with a rising and falling motion;
        "The curtains undulated"; "the waves rolled towards the
        beach" [syn: {roll}, {flap}, {wave}]
     4: increase and decrease in volume or pitch, as if in waves;
        "The singer's voice undulated"