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It's really 'ecky Thump, abbreviated from Hecky Thump. Far as I know, it originated in Yorkshire, or East Lancashire, over a century ago, has no direct meaning, apart from an expression of surprise, or admiration or approval. Rather like Bill's 'Good Lord', and substituted by the God-fearing, Presbetyrian working class, so as to avoid blasphemy and swear words. The word 'Heck', for example, is a substitute for 'Hell', once seen as strong language, even up until the 1960s. Similar to 'Flippin' or 'Flipping', replacing a rather strong word beginning with 'F', or the American 'Shoot', replacing sh*t, and so on.
It's an expression rarely used today though - how times have changed!
Edit: Posted to wrong thread.