Etimology
From Middle English hit-self, equivalent to it + -self.
pronoun
itself (the third person singular, neuter, personal pronoun, the reflexive form of it, masculine himself, feminine herself, gender-neutral themself, plural themselves)
(reflexive) it; A thing as the object of a verb or preposition that also appears as the subject
(emphatic) it; used to intensify the subject, especially to emphasize that it is the only participant in the predicate
(emphatic, archaic) it; used to refer back to an earlier subject
Examples
The door closed by itself
Beautie alone is a ſoveraigne remedy againſt feare,griefe,and all melancholy fits; a charm,as Peter de la Seine and many other writers affirme,a banquet it ſelfe;he gives inſtance in diſcontented Menelaus that was ſo often freed by Helenas faire face: and hTully, 3 Tusc. cites Epicurus as a chiefe patron of this Tenent.
The door itself is quite heavy.
The oil by degrees gets covered with a curdy mass, which after some time settles to the bottom, while itself becomes limpid and colorless.
Related words
synonyms
itsself (obsolete)