This plugin will add a new option Dictionary Mode unter Main Menu > Settings > Taps and gestures.
When enabled, dictionary lookups will be triggered simply by tapping a word.

Please mind that dictionary mode will conflict with other tap actions like page turns.
For page turns, either use your device's hardware buttons (if any) or swiping.

Create a new folder dictionarymode.koplugin inside your KOReader plugins folder and copy all the files from this repository into it. Make sure the plugin is enabled under Main Menu > Options > More Tools > Plugin Management.