E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
To steal or purloin. A filch is a staff with a hook at the end, for plucking clothes from hedges and abstracting articles from shop windows. Probably it is a corruption of pilfer. (Welsh, yspeilio and yspeiliwr; Spanish, pellizcar: French, piller and peler. Filch and pilfer are variants of the same word.
With cunning hast thou filched my daughters heart.