denier n.1

early 14c., "declare to be untrue or untenable," from Old French denoiir "deny, repudiate, withhold," from Latin denegare "to deny, reject, refuse" (source of Italian dinegarre, Spanish denegar), from de "away" (see de-) + negare "refuse, say 'no,' " from Old Latin nec "not," from Italic base *nek- "not," from PIE root *ne- "not."

From late 14c. as "refuse, refuse to grant or give," also "refuse to acknowledge, disavow, disown." Sense of "refuse access to" is from 1660s. Related: Denied; denying.

I may not understand what you say, but I'll defend to your death my right to deny it. [Albert Alligator, "Pogo," Sept. 26, 1951] 

ancient Roman silver coin, 1570s, from Latin denarius, noun use of adjective meaning "containing ten," and short for denarius nummus "the coin containing ten (aces)," from deni- "by tens," from decem "ten" (from PIE root *dekm- "ten"). In English money reckoning, "a penny," this having been, like the Roman denarius, the largest silver coin (hence d for "pence" in l.s.d.).

Proto-Indo-European root meaning "ten."

It forms all or part of: cent; centenarian; centenary; centi-; centime; centurion; century; centennial; cinquecento; dean; deca-; decade; decagon; Decalogue; Decameron; decapod; decathlon; December; decennial; deci-; decile; decimal; decimate; decimation; decuple; decussate; denarius; denier (n.) "French coin;" dicker; dime; dinar; doyen; dozen; duodecimal; duodecimo; eighteen; fifteen; fourteen; hecatomb; hendeca-; hundred; icosahedron; nineteen; nonagenarian; octogenarian; Pentecost; percent; quattrocento; Septuagint; sexagenarian; seventeen; sixteen; ten; tenth; thirteen; thousand; tithe.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit dasa, Avestan dasa, Armenian tasn, Greek deka, Latin decem (source of Spanish diez, French dix), Old Church Slavonic deseti, Lithuanian dešimt, Old Irish deich, Breton dek, Welsh deg, Albanian djetu, Old English ten, Old High German zehan, Gothic taihun "ten."