Plaindre belong to the 3rd
group. Plaindre is a very common french verb.
Plaindre is conjugated the same way that verbs that end in : -ndre
Plaindre is conjugated with auxiliary avoir
Plaindre verb is
French verb plaindre can be conjugated in the reflexive form: Se plaindre
verb is a direct transitive verb, so passive voice can be used.