The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

         Breath vocalized, that is, vibrated and undulated.
                                                  --Holder.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Undulate \Un"du*late\, v. i.
   To move in, or have, undulations or waves; to vibrate; to
   wave; as, undulating air.
   [1913 Webster]

WordNet (r) 3.0 (2006):

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