Hi Jaques,
Is the "Definition" section inactive? Is the arrow to the left of the word "Definition" pointed to the right or down? If it is pointing to the right, try tapping it so that it points down. If the section is still inactive, let me know what book, and the word's location in the book your are attemping to get this information for.
In 1Sam 10, I tried the Look Up then Word Study on the name Gilgal and the words sacrifice and prophecy. When 'Definition' was available it did not show my dictionaries! But it does show a brief definition of unknown source. In the case of 'Definition' being grey and not accessible, I suppose that's another problem as well.
The Logos app has been around for a while, is this considered a long-running bug or glitch? Has Logos acknowledged this as a problem?
Which book/bible is your search coming from? Can you take a screenshot of the results of the Bible Word Study? A screenshot can be taken on iOS by simultaneously pressing the Home button and the Sleep/Wake button; the screen will flash and the picture will be stored in PNG format in the "Camera Roll" on the iPhone or in "Saved Photos" on the iPod touch or iPad.