Stonking: Slang adjective, originally British or Australian, meaning excellent, powerful, impressive, or impressively large.
World Wide Words ("international English from a British viewpoint") calls stonking "a word of vague positive emphasis" with two possible origins: Australia (where stonkered means "drunk") and Britain (where a stonker is "something which is large or impressive of its kind"). The original (19th century) context appears to be the game of marbles, in which a stonk was the marble or the stake put up in a game. During World War II, British military slang appropriated stonk as a noun meaning "intense artillery bombardment" or a verb meaning "to bombard."
The ultimate etymology, suggests the Shorter Oxford English Dictionary, may be onomatopoeic, from the sound of one marble hitting another. The word does not appear to be related to stink.
Stonking (also seen as stonkin' or stonkin) crops up regularly in informal fashion writing, as in this bit of advice about wearing sweater dresses, published in the Guardian in October 2006: "Wear with opaque tights and stonking high heels." (The column also suggests another way to accessorize the sweater dress: "wellies, golden retriever, clandestine lover and a bag of Liquorice Allsorts.")