The Collaborative International Dictionary of English v.0.48:

Chirrup \Chir"rup\, n.
   The act of chirping; a chirp.
   [1913 Webster]

         The sparrows' chirrup on the roof.       --Tennyson.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Chirrup \Chir"rup\, v. t. [imp. & p. p. Chirruped; p. pr. &
   vb. n. Chirruping.] [See Chirp.]
   To quicken or animate by chirping; to cherup.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Chirrup \Chir"rup\, v. i.
   To chirp. --Tennyson.
   [1913 Webster]

         The criket chirrups on the hearth.       --Goldsmith.
   [1913 Webster]

WordNet (r) 3.0 (2006):

chirrup
    n 1: a series of chirps [syn: chirrup, twitter]
    v 1: make high-pitched sounds; "the birds were chirping in the
         bushes" [syn: peep, cheep, chirp, chirrup]