betwen -> between
--- a/src/qtgui/dockfft.ui
+++ b/src/qtgui/dockfft.ui
@@ -794,7 +794,7 @@
       <item row="1" column="2">
        <widget class="QLabel" name="fftOvrLabel">
         <property name="toolTip">
-         <string>FFT buffer overlap betwen two consecutive FFT calculations.</string>
+         <string>FFT buffer overlap between two consecutive FFT calculations.</string>
         </property>
         <property name="text">
          <string>Overlap: 0%</string>
