spat (n.1) Look up spat at
"petty quarrel," 1804, American English, of unknown origin; perhaps somehow imitative (compare spat "smack, slap," attested from 1823).
spat (n.2) Look up spat at
"short gaiter covering the ankle" (usually only in plural, spats), 1779, shortening of spatterdash "long gaiter to keep trousers or stockings from being spattered with mud" (1680s), from spatter and dash (v.).
spat (n.3) Look up spat at
"spawn of a shellfish," especially "spawn of an oyster," also "a young oyster," 1660s, of unknown origin, perhaps from the past tense of spit (v.1).