Re-

CIDE DICTIONARY

Re-,  [L. re-, older form (retained before vowels) red-: cf. F. re-, ré-.].

 A prefix signifying back, against, again, anew; as, recline, to lean back; recall, to call back; recede; remove; reclaim, to call out against; repugn, to fight against; recognition, a knowing again; rejoin, to join again; reiterate; reassure. Combinations containing the prefix re- are readily formed, and are for the most part of obvious signification.  [1913 Webster]

OXFORD DICTIONARY

Re-, prefix.
1 attachable to almost any verb or its derivative, meaning: a once more; afresh, anew (readjust; renumber). b back; with return to a previous state (reassemble; reverse).

Usage

A hyphen is normally used when the word begins with e (re-enact), or to distinguish the compound from a more familiar one-word form (re-form = form again).
2 (also red- before a vowel, as in redolent) in verbs and verbal derivatives denoting: a in return; mutually (react; resemble). b opposition (repel; resist). c behind or after (relic; remain). d retirement or secrecy (recluse; reticence). e off, away, down (recede; relegate; repress). f frequentative or intensive force (redouble; refine; resplendent). g negative force (recant; reveal).

Etymology

L re-, red-, again, back, etc.