narrow-based security index
(B) Without taking into account any portion of the index composed of exempted securities as defined in section 3(a)(12) of the Securities Exchange Act of 1934 (15 U.S.C. 78c(a)(12)), as in effect on the date of enactment of the Futures Trading Act of 1982 (other than any municipal security as defined in section 3(a)(29) of the Securities Exchange Act of 1934 (15 U.S.C. 78c(a)(29))), the remaining portion of the index would be within the term narrow-based security index under paragraph (1)(i) of this definition.
17 CFR § 1.3
Words used in the singular form in the rules and regulations in this chapter shall be deemed to import the plural and vice versa, as the context may require. The following terms, as used in the Commodity Exchange Act, or in the rules and regulations in this chapter, shall have the meanings hereby assigned to them, unless the context otherwise requires: