UK, 1871—a paper bag, balloon, etc., filled with flour and thrown or dropped such that it bursts and disperses its contents over the target on impact, usually as a prank or as part of a protest or public demonstration
to urinate—slang—2nd half of the 20th century—based on the sound /eɪn/, common to the verb, adjective and noun that compose it—‘main vein’ probably refers to the penis
1843—a representation of a human skull or skeleton, originally crafted from sugar and intended to be eaten and often given to children as a gift around Día de Muertos (Day of the Dead)