Very simple words; terms that are easy to understand. You're an astrophysicist and I'm not, so please, explain this concept in words of one syllable so I might have a chance of understanding it!
if you explain something in words of one syllable, you do it in words that are very simple and easy to understand because the person you are speaking to is stupid
Usage notes: A syllable is a unit of sound that is made by a combination of letters. Words which only have one syllable are short and simple.
I was trying to explain to him again, in words of one syllable, why safety regulations must be obeyed at all times.