[…] the lexicon is a set of 'lexical entries', each lexical entry being a pair ('D','C'), where 'D' is a phonological distinctive feature matrix "spelling" a certain lexical formative and 'C' is a collection of specified syntactic features (a complex symbol).
- Chomsky (1969), Pag. 84

[…] the lexical entry must specify: (a) aspects of phonetic structure that are not predictable by general rule [...] (b) properties relevant to the functioning of transformational rules [...] (c) properties of the formatives that are relevant for semantic interpretation [...] (d) lexical features indicating the positions in which a lexical formative can be inserted (by the lexical rule) in a preterminal string. In short, it contains information that is required by the phonological and semantic components of the grammar and by the transformational part of the syntactic component of the grammar, as well as information that determines the proper placement of lexical entries in sentences, and hence, by implication, the degree and manner of deviation of strings that are not directly generated.
- Chomsky (1969), Pag. 87

We might, then, take a lexical entry to be simply a set of features, some syntactic, some phonological, some semantic.
- Chomsky (1969), Pag. 214