re-

The Latin prefix rĕ- is from Proto-Italic *wre (“again”), which has a parallel in Umbrian re-, but its further etymology is uncertain (OED). While it carries a general sense of "back" or "backwards", its precise sense is not always clear, and its great productivity in classical Latin has the tendency to obscure its original meaning.

Watkins proposes a metathesis of Proto-Indo-European *wert- (“to turn”), while de Vaan suggests Proto-Indo-European *ure- (“back”), which may be found in Proto-Slavic *rakъ (“crayfish, lobster”) (tentatively, in an original sense *“looking backwards”) and Albanian rrë-(“back”, preverb), unless the latter is borrowed from Latin.

Prefix

re-

1. back, backwards
2. un-, de-

   ‎re- + ‎glūtinō (“glue”) → ‎reglūtinō (“unglue, separate”)

   ‎re- + ‎neō (“spin, weave, entwine”) → ‎reneō (“unspin, unravel”)

   ‎re- + ‎gelō (“freeze, congeal”) → ‎regelō (“thaw, unfreeze”)

3. again; prefix added to various words to indicate an action being done again, or like the other usages indicated above under English.