They said they'd help us, but then finked out.
- To withdraw; back out.
- To fail.
Idioms and Phrasal Verbs
Origin of fink
- Perhaps from German student slang Fink student not belonging to a student association (from German finch) (akin to Old English finc) or perhaps from such German compounds as Schmutzfink dirty person, mudslinger Schmutz filth Fink finch (perhaps influenced by Rotwelsch (German underworld argot) Fink, Pink man) (akin to Frisian pink little finger, penis)
From American Heritage Dictionary of the English Language, 5th Edition