according to Wickipedia
Spotted dick is a steamed suet pudding, popular in Britain, containing dried fruit (usually currants or raisins) commonly served with custard. Spotted refers to the dried fruit (which resemble spots) and dick may be a contraction or corruption of the word pudding (from the last syllable) or possibly a corruption of the word dough[1] or dog, as "spotted dog" is another name for the same dish with the use of plums rather than currants. Another explanation offered for the word "dick" is that it is the German word for "thick."