Is it ensure, insure, or assure?
Old English crammian "press something into something else," from Proto-Germanic *kram-/*krem- (cf. Old High German krimman "to press, pinch," Old Norse kremja "to squeeze, pinch"), from PIE root *ger- "to gather" (cf. Sanskrit gramah "heap, troop," Old Church Slavonic gramota "heap," Latin gremium "bosom, lap"). Meaning "study intensely for an exam" originally was British student slang first recorded 1803. Related: Crammed; cramming.
: a cram session/ cram booknoun
A very diligent student; grind (1900s+)verb
To study intensively for an upcoming examination (1803+ British students)