It might defunk.Wooohoooo, reanalysis in action! Reanalysis is when someone interprets the structure (or meaning, etc) of a word or phrase differently from previous speakers. This can result in widespread permanent change to the language in question, and in fact is how much language change takes place. For instance, we all know that apron and adder were originally napron and nadder, but because a nadder is identical to an adder when it's spoken, people reanalysed it as the latter. Ditto peas and cherries, which are now the plural forms of the singular pea and cherry, but when they were first borrowed from French they were pease and cherise - mass nouns. We still have pease pudding and the colour word cerise (that one was probably borrowed again later on, though).
The reanalysed word in question is defunct, meaning something like 'not working'. This comes from Latin, literally meaning 'not working' (dēfunctus, with the prefix de- and the past participle of fungī 'to perform', says the OED). We don't really think about the etymology when we use it though, especially if we don't know Latin, which most people don't. So it's just a word that means 'not working' or 'not in use'.
The reanalysis has come about because the word-final consonant /t/ sounds just like the past participle ending -ed. (This is because -ed can sound like /d/ or /t/ depending on the sound it follows.) Therefore, defunct sounds exactly like defunked. Defunked doesn't exist (with this meaning), but it follows the pattern for verbs in English, with a regular past tense ending. So we can postulate that the word is the past participle of defunk. If that's the case, the verb can be used in all its forms, including the bare stem form used in the original example, defunk.
The process I've hypothesised here takes a word which is used in its current form as an adjective and reanalyses it back into its past participle form (possibly even complete with negative prefix on the root funk) from whence it came!
(By the way, clever people have of course spotted the potential for the word as a band name, so it's hard to google for other examples. But the fact that hits for this interpretation don't outweigh the band's hits shows that this is either non-existent or very rare so far. In addition, Urban Dictionary notes the verb with the meaning 'to remove funk [dirt]' or 'to make less funky', both predictable meanings of de-+funk.)