index fossil index forest • index fund · · · Info · Definitions · Synonyms · Characters · · index fossil · · Text Common · · Latin · · Scripts 12 · · Length 4 · · Syllables Definitions · · · (noun) a fossil known to have lived in a particular geologic age that can be used to date the rock layer in which it is found. Synonyms: index fossil, guide fossil. · · Noun Definition 1 Synonyms · · · guide fossil · · Synonym 1 Characters · · space U+0020 d latin small letter d U+0064 e latin small letter e U+0065 f latin small letter f U+0066 i latin small letter i U+0069 l latin small letter l U+006C n latin small letter n U+006E o latin small letter o U+006F s latin small letter s U+0073 x latin small letter x U+0078