ream (n.1) Look up ream at Dictionary.com
measure of paper, mid-14c., from Old French reyme, from Spanish resma, from Arabic rizmah "bundle" (of paper), from rasama "collect into a bundle." The Moors brought manufacture of cotton paper to Spain.

Early variant rym (late 15c.) suggests a Dutch influence (compare Dutch riem), probably borrowed from Spanish during the time of Hapsburg control of Holland. For ordinary writing paper, 20 quires of 24 sheets each, or 480 sheets; often 500 or more to allow for waste; slightly different numbers for drawing or printing paper.
ream (v.) Look up ream at Dictionary.com
"to enlarge a hole," 1815, probably a southwest England dialectal survival from Middle English reme "to make room, open up," from Old English ryman "widen, extend, enlarge," from Proto-Germanic *rumijan (cognates: Old Saxon rumian, Old Norse ryma, Old Frisian rema, Old High German rumen "to make room, widen"), from *rumaz "spacious" (see room (n.)). Slang meaning "to cheat, swindle" first recorded 1914; anal sex sense is from 1942. To ream (someone) out "scold, reprimand" is recorded from 1950.
ream (n.2) Look up ream at Dictionary.com
"cream" (obsolete), Old English ream, from Proto-Germanic *raumoz (cognates: Middle Dutch and Dutch room, German Rahm), of uncertain origin.