a. [f. THUNDER sb. + -LESS.] Unaccompanied by thunder (or noise like thunder).

1

1821.  Newbern (NC) Sentinel, 19 May, 3/3.

        ’Tis past!—the flash that burst the gloom
  Of Europe’s darken’d sky,
Has vanish’d thunderless—and Rome
  Sighs amid Slavery.

2

1855.  G. Meredith, Shav. Shagpat (1850), 371. Flashes of thunderless lightnings.

3

1880.  Tennyson, Voy. Maeldune, iii. The long waterfalls Pour’d in a thunderless plunge to the base of the mountain walls.

4