As part of the word “spruce,” there is “Pruce”. This was an old form of the designation of the former (1525-1935) Germanic nation known as Prussia.

An expression like “das Pruce” evolved to refer to the region’s main evergreen tree (aka Prussian fir) with the preceding word “s” misinterpreted for being part of the word; thus making “spruce.”   

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Well I’ve never heard that explanation before!