Abarim Publications' online Biblical Greek Dictionary
The noun δηναριον (denarion) is the Greek transliteration of the Roman denarius (plural: denarii), a day's wage for a low ranking soldier or common laborer (Matthew 20:2), and the principle unit of account of the Roman economy. The oil that Mary poured over Jesus' feet was worth 300 dinari; about a year's wage (Mark 14:5, John 12:5).
The word denarius is a nominalized adjective, formed from the term deni, meaning ten at a time (a reference to a copper coin worth 0.1 denarius), which in turn comes from deceni, from decem, ten, plus the suffix -arius, which forms adjectives from numerals. It literally means "containing ten things" (which, to Jewish intuition, may have reminded of the Ten Commandments of the Law, the Ten Plagues of Egypt or the ten camels of Abraham). It's used 16 times in the New Testament; see full concordance.
Also see our article on αργυρος (arguros), meaning silver or money.