What's the plural form of retrograde motion? Here's the word you're looking for.
Answer
The noun retrograde motion can be countable or uncountable.
In more general, commonly used, contexts, the plural form will also be retrograde motion.
However, in more specific contexts, the plural form can also be retrograde motions e.g. in reference to various types of retrograde motions
or a collection of retrograde motions.
