Phrase used when advising somebody of facts /an issue /and explanation (etc) using the most simplest of words in order that they may understand.
Often associated with 'full and frank conversation' the phrase 'words of one
syllable or less' is actually gramatically incorrect in its use of 'or less' (essentially 'or less' makes no sense whereas 'or fewer' would be correct) but nicely conveys the situation.
Believed to have originated with the staff of
Britain's railways in
Southern England.
"What do you mean
Bert has
done it wrong again?
I'd better go and explain how to do it in
words of one syllable or less"