enumitem.sty not found

As said in the comments, BasicTeX contains what is strictly necessary for TeX and LaTeX to work, and very little more.

If you don't want to install the full MacTeX (which is the full TeX Live, adapted for Mac OS X) and if you want to stick to BasicTeX, you can install the enumitem package yourself. The simplest way to do it is to use the TeX Live Utility program, which comes with the MacTeX-additions (everything of MacTeX excepted TeX Live). BTW, it is strongly recommended to install these MacTeX-additions together with BasicTeX, if only to install the packages you think are missing…

This worked for me.

sudo tlmgr install enumitem

In case if tlmgr is not found edit .bash_profile using vim ~/.bash_profile

and add these lines

### TeX
export PATH="/Library/TeX/Distributions/.DefaultTeX/Contents/Programs/texbin:$PATH"

Run source ~/.bash_profile

And then run the above command.