noun

• (Roman mythology) The god of doorways, gates and transitions, and of beginnings and endings, having two faces looking in opposite directions.
• (attributively) Used to indicate things with two faces (such as animals with diprosopus) or aspects; or made of two different materials; or having a two-way action.
• (chemistry, attributively) Used to indicate an azo dye with a quaternary ammonium group, frequently with the diazo component being safranine.
• (figuratively) A two-faced person, a hypocrite.
• A moon of Saturn.