Is it ensure, insure, or assure?
"first-rate, excellent," 1837, from prefix in superfine (1682), denoting "highest grade of goods," from Latin super "above, over, beyond" (see super-). Extended usage as a general term of approval is 1895 slang, revived 1960s. Rhyming reduplication form super-duper first attested 1940.
word-forming element from Latin adverb and preposition super "above, over, on the top (of), beyond, besides, in addition to," from PIE *uper "over" (cf. Sanskrit upari, Avestan upairi "over, above, beyond," Greek hyper, Old English ofer "over," Gothic ufaro "over, across," Gaulish ver-, Old Irish for), comparative of root *upo "under."
Above; over; upon: superstructure.
Superior in size, quality, number, or degree: supersonic.
Exceeding a norm: supersaturate.
Excessive in degree or intensity: superexcitation.
Containing a specified ingredient in an unusually high proportion: superoxide.
A law requiring that meetings of legislative bodies be opened to the public: After the sunshine law the city council had to open its doors (1972+)
One who likes to sit in the sun, esp to get a tan: turns sun-worshipper in April (1966+)
A superintendent, esp one who is custodian of an apartment building (1857+)