Turn off line wrap in Gedit

Edit > Preferences > View Tab > Text Wrapping options right there, front and center. Not "well hidden" by any means.

UPDATE:

In 3.14.3 (and perhaps earlier) and in newer versions of gedit, there is a "Text wrapping" checkbox when you click on the "Line/Column" indicator on the status bar, in bottom right corner of the window.

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IN VERY OLD VERSIONS:

As of gedit 10.4, there is no preferences dialog anymore. Some of the options are now in the status bar, but not word-wrapping.

You can turn word wrapping off by tweaking the GSettings settings. To do so, run the following command in your terminal:

gsettings set org.gnome.gedit.preferences.editor wrap-mode none

Besides none, you can also turn it back on with either word, char, or word-char word wrapping.