syntactic index
Technical term in linguistics referring to an index used in syntactic analysis, such as a subscript or superscript marking grammatical relations.
In generative grammar, syntactic indices are sometimes used to represent phrase structure.
Compound of 統語 (tōgo, 'syntax') and 指標 (shihyō, 'index'). The exact historical derivation is uncertain; the term is a modern technical coinage in linguistics.