WordNet sense 1 (a brief period of precipitation):

rain shower

WordNet sense 2 (someone who organizes an exhibit for others to see):

exhibitor, exhibitioner

WordNet sense 3 (a sudden downpour (as of tears or sparks etc) likened to a rain shower):

cascade

WordNet sense 4 (rain abundantly):

shower down

WordNet sense 5 (expend profusely; also used with abstract nouns):

lavish

WordNet sense 6 (washing yourself by standing upright under water sprayed from a nozzle):

shower bath