Wordorigins.org

Adams, Michael (2003). Slayer slang: a Buffy The Vampire Slayer lexicon. Oxford, Oxford University Press.

A comprehensive treatise on the slang and usage of this inventive television series.

A round robin is a type of sports tournament where all the players play one another in succession. This sense comes from an older, nautical jargon term referring to a document signed by mutineers. In a round robin document, the mutineers would sign their names in a circle, so the authorities could not identify the first to sign, who presumably would be the ring leaders. (Despite the temptation to connect round robin and ringleader, the two words are etymologically unconnected.) Some sources suggest that this usage of round robin comes from the French rond ruban, or round ribbon, that was tied around these petitions--but little evidence exists to support this guess. From the Weekly Journal of 3 January 1730:

A Round Robin is a Name given by Seamen, to an Instrument on which they sign their Names round a Circle, to prevent the Ring-leader being discover’d by it, if found.

The origin of the name of this Jamaican musical style is unknown. Credit for coining the word goes to Toots Hibbert for his 1968 song Do the Reggay. Some suggest it comes from the Jamaican English rege-rege meaning quarrel or row. Others indicate that it is from raggedy a reference to a quality of the musical style.

From an advertisement in the 7 September 1968 Daily Gleaner of Kingston, Jamaica:

Come do this brand new dance THE REGGAE.

(Source: Oxford English Dictionary, 2nd Edition; Newspaperarchive.com)

To rain cats and dogs is to rain very heavily. The metaphor behind the phrase is that of a dog and a cat fighting, something noisy and violent. The metaphor of a storm resembling a dog and cat fight dates to the mid-17th century, although the phrase, as we know it today, doesn’t appear for another half century. Henry Vaughn’s Olor Iscanus of 1651 goes:

The Pedlars of our age have business yet,
And gladly would against the Fayr-day fit
Themselves with such a Roofe, that can secure
Their Wares from Dogs and Cats rain’d in showre

Pussyfoot, which means a delicate, soft step comes from the imagery of a cat’s careful tread. To pussyfoot is to proceed with caution, subtlety, and delicacy and is used pejoratively. The term is American in origin and, in adjectival form, dates to at least 1893. From Scribner’s Magazine of November of that year:

Men who were beginning to walk pussy-footed and shy at shadows.