While it may sound like cuss-word, shittim is merely the plural of shittah, a Hebrew term for a kind of desert tree (Isa 41:19, see here). Many identify this tree with the Acacia family, a genus with more than a thousand species.
In the desert areas of the biblical heartland, one can find the Acacia tortillis or the Umbrella thorn. These trees are short and twisted with a characteristic flat top. Thorns and tiny leaves grace its branches.
According to texts like Exo 25:10-13 (see here) or Deut 10:3 (see here) the furniture produced for Israel's tabernacle (including the Ark of the Covenant) was made from shittim wood. Only a skilled artisan could work in this medium!