The most basic form of address is “Tan” for junior monks and “Ajahn” for senior monks.
Sāmaṇera (Pāli) / Nehn (Thai): A novice monk. Most Thai sāmaṇeras are young boys, as men older than twenty take full bhikkhu ordination directly. However, Ajahn Chah instituted a period of sāmaṇera training before granting full ordination.
Bhikkhu (Pāli: monk, literally one who eats almsfood): A fully-ordained Buddhist monk.
Phra (Thai: Venerable): A respectful formal salutation used for any monk.
Phra Khru (Thai: Venerable teacher)
‘Phra’ means ‘venerable, sacred, excellenet‘; ‘Khru’ (from Sanskrit guru) means ‘teacher’.
Luang Por (Thai: Venerable Father): A term of veneration used for very senior monks.
Luang Pu (Thai: Venerable Paternal Grandfather): Even more senior than Luang Por.
Mahā (Pāli: great): A prefix added to the name of a monk who has completed the third degree of Pāli studies.
Chao Khun (Thai): A title given to monks selected by the Thai Sangha authorities to acknowledge special past acts of service. The King of Thailand bestows these titles himself.
Mae Chee (Thai): A white-robed nun who keeps eight precepts.
Pakow (Thai) /Anāgārika (Pāli): A white-robed male monastery attendant or postulant who keeps eight precepts.
Upasaka (male) / Upasika (female) (Pāli: one who draws close): A committed Buddhist lay disciple.
– Adopted from Abhayagiri.org