Onomatopoeia. Connected with splash and splosh by vowel apophony (sound change); compare with Indo-European ablaut as in sing/sang/sung/song.
splish (plural splishes)
- (onomatopoeia, humorous) splash
splish (third-person singular simple present splishes, present participle splishing, simple past and past participle splished)
- (intransitive) To make a light splashing sound.