In Turkish the suffix -(İ)ş is attached to transitive and intransitive verbs
and it conveys a meaning of an action being done together.
When it combines with a transitive verb like öpmek, to kiss, it shows reciprocity.
|John Mary'yi öptü, Mary John'u öptü. Öpüştüler.
|| John kissed Mary, Mary kissed John. They kissed.
Some verbs in Turkish have -(İ)ş at the end by default, and they cannot take another -(I)ş.
For example barışmak means to make peace, and there is no barışışmak.
Also some other verbs like tutmak (to hold, to keep) can take -(İ)ş but they can have a very different meaning,
tutuşmak means to catch fire. Therefore you need to be careful when using this suffix, it might not mean what you think it means.