Gopher wood is not related to the gopher of North America.
Some have suggested that because of the wood used in many ancient ship building methods, this refers to cypress, and because of the similarity in sound. Some say cedar because of its great durability.
In the Greek translation Septuagint (LXX), it is xylon tetragonon, "squared timber”
The Latin Vulgate rendered it as lignis levigatis "smoothed (possibly planed) wood". When I was investigating this, I realized that I had never noticed how similar the Hebrew letters gimel (g) and the kaf (k) are to each other. A minimal scribal error could have caused such a reading.
|Third Hebrew letter - gimel = g|
|Eleventh Hebrew Letter - kaf = k|
The words gopher גפר and kofer כפר (pitch) are very close, and possibly suggests “pitched, or caulked wood.”
To me, this makes much more sense than something that we can't (with reliability) even define. You judge, but perhaps it does not make much difference either way. It is interesting though.