Is it ensure, insure, or assure?
word-forming element meaning "under," from Latin preposition sub "under" (also "close to, up to, towards"), from a variant form (*(s)up-, perhaps representing *ex-upo-) of PIE root *upo- "from below," hence "turning upward, upward, up, up from under, over, beyond" (cf. Sanskrit upa "near, under, up to, on," Greek hypo "under," Gothic iup, Old Norse, Old English upp "up, upward," Hittite up-zi "rises"). Used as a prefix and in various combinations.
The original meaning is now obscured in many words from Latin ( suggest, suspect, subject, etc.). The prefix is active in Modern English, sometimes meaning "subordinate" (as in subcontinent, first recorded 1863) or "inferior" (a sense first attested 1963).
Below; under; beneath: subcutaneous.
Subordinate; secondary: subinfection.
Less than completely or normally; nearly; almost: subfertility.
A prefix that means "underneath or lower" (as in subsoil), "a subordinate or secondary part of something else" (as in subphylum.), or "less than completely" (as in subtropical.)
To block or thwart; frustrate: Instead, the drive toward integration has been stymied by the speed-bump of crime
[1857+ Golf; origin uncertain; perhaps fr British dialect stimey, ''dim-sighted person,'' fr stime, ''ray or bit of light''; adopted in golf for situations where the player or, as it were, the ball cannot ''see'' a clear path ahead]
Excellent; fine; coolnoun
Smooth skill; polished adroitness: He has plenty of suave when it comes to girlsverb
: Then I took her off her feet. I suaved her/ I guess old Buck suaved her off her feet (1960s+ Teenagers)
A substitute of any sort, esp an athlete who replaces another or an athlete not on the first team (1830+)verb
: Who'll sub for me when I go on leave? (1853+)