Reciprocal action is when there is mutual action between two parties as in: My sisters were talking to each other. The “to each other” idea is the meaning of reciprocal.
The word ἀλλήλων is the word used. It is almost always found in the oblique cases of the plural.
Nominative (none) (none)
Genitive (none) ἀλλήλων
Dative (none) ἀλλήλοις/αις
Accusative (none) ἀλλήλους/ας
See hitpael.