learn Astronomy Dictionary from Astronomy Dictionary app
This app is very user-friendly, as it offers an easy search function plus text to speech: just listen to the definition, instead of reading it.
The screen is visually clear and offers a detailed but still understandable explanation. You may also set another theme colour.
You can determine some terms as your favourites and collect them seperately. This feature can be managed easily. If there are terms, expressions or idioms which you would like to add, do it, so that you can look them up, whenever you want. Thanks to the unlimited ability of adding new words.