Épaissir belong to the 2
nd group. Épaissir is a common french verb.
Épaissir is conjugated the same way that verbs that end in :
-ir
Épaissir is conjugated with
auxiliary avoir.
Épaissir verb is
direct transitive, intransitive.
French verb épaissir can be conjugated in the reflexive form:
S'épaissir
Épaissir verb is a direct transitive verb, so passive voice can be used.