underlying or underlier
An option or a future is a right or a commitment to buy or sell something at a future date. The underlying is the financial instrument that may or must be bought or sold in each option or futures contract. FAS 133, as amended by FAS 149, defines an underlying to be a specified interest rate, security price, commodity price, foreign exchange rate, index of prices or rates, or other variable (including the occurrence or nonoccurrence of a specified event such as a scheduled payment under a contract). An underlying may be a price or rate of an asset or liability but not the asset or liability itself. American Banker Glossary
Financial and business terms. 2012.