There are only two reciprocal pronouns: each other and one another. The reciprocal pronouns are used to express a relationship in which the same thing is done by each of two parties towards the other or more parties towards others. For example, Jack is smiling at Jill and Jill is smiling at Jack. This is the same as Jack and Jill are smiling at each other. The smile is reciprocated by the other.
The reciprocal pronouns refer mostly to people, but they can also be applied to animals or things. Each other is usually used when writing or speaking about two people or things. For more than two people or things, one another is generally used, but it is not a rule that must be strictly followed.
A reciprocal pronoun is used to shorten a long sentence by not repeating the same action done by two or more people.
The subject has to be plural for the reciprocal pronouns to be used
Reciprocal pronouns can be objects of verb
Reciprocal pronoun following preposition
Reciprocal pronouns in possessive case.