The sense index file lists all of the senses in the WordNet database with each line representing one sense. The file is in alphabetical order, fields are separated by one space, and each line is terminated with a newline character.

Each line is of the form:

sense_key~~synset_offset~~sense_number~~tag_cnt

sense_key is an encoding of the word sense. Programs can construct a sense key in this format and use it as a binary search key into the sense index file. The format of a sense_key is described below.

synset_offset is the byte offset that the synset containing the sense is found at in the database "data" file corresponding to the part of speech encoded in the sense_key. synset_offset is an 8 digit, zero-filled decimal integer, and can be used with fseek(3) to read a synset from the data file. When passed to the WordNet library function read_synset() along with the syntactic category, a data structure containing the parsed synset is returned.

sense_number is a decimal integer indicating the sense number of the word, within the part of speech encoded in sense_key, in the WordNet database. See wndb(5WN) for information about how sense numbers are assigned.

tag_cnt represents the decimal number of times the sense is tagged in various semantic concordance texts. A tag_cnt of 0 indicates that the sense has not been semantically tagged.

A sense_key is represented as:

lemma%lex_sense

where lex_sense is encoded as:

ss_type:lex_filenum:lex_id:head_word:head_id

lemma is the ASCII text of the word or collocation as found in the WordNet database index file corresponding to pos. lemma is in lower case, and collocations are formed by joining individual words with an underscore (_) character.

ss_type is a one digit decimal integer representing the synset type for the sense. See below for a listing of the numbers corresponding to each synset type.

lex_filenum is a two digit decimal integer representing the name of the lexicographer file containing the synset for the sense. See lexnames(5WN) for the list of lexicographer file names and their corresponding numbers.

lex_id is a two digit decimal integer that, when appended onto lemma, uniquely identifies a sense within a lexicographer file. lex_id numbers usually start with 00, and are incremented as additional senses of the word are added to the same file, although there is no requirement that the numbers be consecutive or begin with 00. Note that a value of 00 is the default, and therefore is not present in lexicographer files. Only non-default lex_id values must be explicitly assigned in lexicographer files. See wninput(5WN) for information on the format of lexicographer files.

head_word is only present if the sense is in an adjective satellite synset. It is the lemma of the first word of the satellite's head synset.

head_id is a two digit decimal integer that, when appended onto head_word, uniquely identifies the sense of head_word within a lexicographer file, as described for lex_id. There is a value in this field only if head_word is present.

The synset type is encoded as follows:

1	NOUN
2	VERB
3	ADJECTIVE
4	ADVERB
5	ADJECTIVE SATELLITE