MEANING: conjunction: Before (earlier in time).

ETYMOLOGY: From Old English aer (earlier). Ultimately from the Indo-European root ayer- (day, morning), which is also the source of early and erst (as in erstwhile). Earliest documented use: 822.

MR. E. - a puzzlement

R. R. E. - a mechanical model of the Solar System

T. R. E. (preferably with a German accent) - a hypothesis, or (after a while) the best explanation we have for a set of observations

RE - That's about it.