Hieromonk (Greek: Ἱερομόναχος, Ieromonachos; Slavonic: Ieromonakh, Romanian: Ieromonah), also called a Priestmonk, is a monk who is also a priest in the Orthodox Church and Eastern Catholicism.
A hieromonk can be either a monk who has been ordained to the priesthood or a priest who has received monastic tonsure. When a married priest's wife dies, it is not uncommon for him to become a monk, since the Church forbids clergy to enter into a second marriage after ordination.
Ordination to the priesthood is the exception rather than the rule for monastics, as a monastery will usually only have as many hieromonks and hierodeacons as it needs to perform the daily services.
In the church hierarchy, a hieromonk is of higher dignity than a hierodeacon, just as a secular (i.e., married) priest is of higher dignity than a deacon. Within their own ranks, hieromonks are assigned order of precedence according to the date of their ordination. Ranking above Hieromonk is a Hegumen and an Archimandrite.
Read more about Hieromonk: Forms of Address, In Other Countries and Western Christianity