The Collaborative International Dictionary
Sur-
Sur- \Sur-\ [F. sur over, above, contr. fr. L. super, supra. See Super-.] A prefix signifying over, above, beyond, upon.
Douglas Harper's Etymology Dictionary
sur-
word-forming element meaning "over, above, beyond, in addition," especially in words from Anglo-French and Old French, from Old French sour-, sor-, sur-, from Latin super (see super-).
sur-
assimilated form of sub- before -r-.
Wiktionary
sur-
pre. (context not currently productive English) {{non-gloss definition|A syncopic variant of ''(l en super-)''.}}