They started as same word, but their meanings have drifted apart over time.
What about Day Tomorrow?
English was never the same after the Norman Conquest
'Poets laureate'? 'Court-martials'? The curious history of postpositive adjectives in English.
Some practical guidance, and interesting history, about a common mistake.
There, there. We'll sort it out.
A simple way to keep them apart. (Most of the time.)