certain — If you are certain about something, you firmly believe it is true and have no doubt about it. If you are not certain about something, you do not have definite knowledge about it.
merton — Robert King, 1910–2003, U.S. sociologist.
Three-syllable rhymes
for certain — free from doubt or reservation; confident; sure: I am certain he will come.
uncertain — not definitely ascertainable or fixed, as in time of occurrence, number, dimensions, or quality.
