This form began to replace the old third person plural pronoun, .sn, from c.1400 BCE. This process started with the objects of prepositions and then instances of the pronoun attached to jw. By Late Egyptian it was the standard form outside of the most formal texts, which retained .sn.
This form of pronoun attaches directly to the preceding word, and means different things depending on what it is attached to.
When attached to a noun, it indicates the possessor of the noun.
When attached to a verb of the suffix conjugation, it indicates the subject of the verb.
When attached to an infinitive verb (especially of an intransitive verb) whose subject is not otherwise expressed, it indicates the subject of the verb.
When attached to a transitive infinitive verb whose subject is otherwise expressed or omitted, it indicates the object of the verb.
In the third person, when attached to a prospective participle, it indicates gender and number agreement.
When attached to a particle like jw or a parenthetic like ḫr, it indicates the subject of the clause.
When attached to a preposition, it indicates the object of the preposition.
When it follows a relative adjective such as ntj or ntt, it indicates the subject of the relative clause (except in the first person singular and third person common).
Some authors distinguish between the singular and plural as two different morphemes, treating plural .w as a variant of Old Egyptian .wy or *.wj and singular .w as a variant of Old Egyptian .j; however, at least by Middle Egyptian, no distinction seems to have been made.
In Old Egyptian, .w and its variants were used for the masculine plural, while .tj and its variants were used for the feminine plural. By Middle Egyptian, .w had taken on both roles, making plural .tj rare.
This suffix, when written at all, is often written before the determinative of the verb.