You can set a special word-tap action accessed by tapping on a word.
You can have this feature active all the time, so that whenever you
tap on a word other than one in a hyperlink the action is activated,
or you can activate it on demand for the next tap via
View|Lookup word or by binding the Lookup word
action to a key, graffiti gesture, etc.
To use the Lookup in PPI option, you need to have
the Plucker Plugin Interface (PPI) and a compatible dictionary
installed and configured (see refsec:PPI).