How to turn off automatic spellcheck

Hi all! I'm sure there's a very simple answer, but I just can't figure it out. I want to turn OFF auto spellcheck so that I don't have the red squiggly line under a lot of words I'm using in my file. I thought I could just go to Edit > Spelling > Auto Spell Check and UNCHECK that choice. But... it won't turn off. I can choose "Check Spelling" and it does... but then it goes right back to auto spellcheck. I'm using Version 25.0 on my iMac. What can I do to make it stop automatically spellchecking?