What is the meaning and origin of the "se-" prefix?

Question

There are a lot of Latin words that begin with se-. It adds the notion of being "apart" or "separated":

• secerno
• secludo
• secubo
• seduco
• seiungo
• sepono
• etc.

The linked entry calls it an "inseparable prefix" meaning "aside / by itself." Wiktionary associates it with the reflexive pronoun se. There also seems to be a separate (apparently unrelated) meaning where se is a contraction of sine, e.g. securus = sine cura.

These options provoked some questions for me:

• If se- is related to the reflexive pronoun, how do we make sense of the "apart" meaning?
• If se- is a preposition, why does it only appear as a prefix? It reminds me of secus, but seems to have the opposite meaning.

Answer 1

There is a (rare) preposition sēd, sē “without” with the ablative (as in Old Latin sed fraude), and (more commonly) a prefix sē- “without, apart from” (as in securus etc.), and also the conjunction sed “but”. The commonly accepted theory is that these derive from some case form (ablative?) of the reflexive pronoun IE *swe-, as in Latin se, suus. The semantic development would have been something along the lines of “on one’s own” > “without”.