From the second edition (1989):

cometary, a.

(ˈkɒmɪtərɪ) [f. comet or L. comēta + -ary, after planetary, in late L. planētārius. Cf. F. cométaire.]

1. Of or pertaining to a comet or comets.

1652 Gaule Magastrom. 79 The prodigious aspects in the heavens (planetary, as well as cometary). 1748 Hartley Observ. Man ii. iv. 400 Revolutions either in a planetary or a cometary Orbit. 1787 Smeaton in Phil. Trans. LXXVII. 319 note, A similar instrument to be made for cometary‥observations. 1853 Herschel Pop. Lect. Sc. iii. §42. (1873) 126 Few persons at all acquainted with cometary history.

2. Of the nature of a comet; comet-like.

1847 De Quincey Wks. (1862) VII. 53 Their [coaches'] periods of revolution were so cometary and uncertain. 1869 Phillips Vesuv. iii. 85 Cometary or star-like meteors. 1873 E. Dowden in Contemp. Rev. July 176 This cometary apparition‥where lies its nucleus? and is its orbit ascertainable? What is Victor Hugo?