The Collaborative International Dictionary of English v.0.48:

Rainy \Rain"y\ (r[=a]n"[y^]), a. [AS. regenig.]
   Abounding with rain; wet; showery; as, rainy weather; a rainy
   day or season.
   [1913 Webster]

WordNet (r) 3.0 (2006):

rainy
    adj 1: (of weather) wet by periods of rain; "showery weather";
           "rainy days" [syn: showery, rainy]

Moby Thesaurus II by Grady Ward, 1.0:

48 Moby Thesaurus words for "rainy":
   angry, blinding, boggy, cat-and-doggish, cloudy, cyclonic, damp,
   dampish, dank, dewy, dirty, drippy, driving, drizzling, drizzly,
   drumming, fenny, foul, humid, marshy, misty, misty-moisty, mizzly,
   moist, muggy, pelting, pluvial, pluviose, pluvious, pouring,
   raging, roric, roriferous, showery, sticky, storming, stormy,
   streaming, swampy, tacky, tempestuous, tornadic, turbulent,
   typhonic, typhoonish, undried, wet, wettish