Thai royal ranks and titles

The precedence of Thai royalty follows a system of ranks known as thanandon (), which are accompanied by royal titles.
The Sovereign.
There are two styles which can be used for a king in ordinary speech, depending on whether he has been crowned:
Consorts.
Traditionally, titles of royal wives depended on their birth titles and royal favour; only princesses of high birth (Chao Fa, Phra Ong Chao and Mom Chao Ying) assuming titles higher than Chao Chom. There were no clear rules about the hierarchy of titles above Chao Chom until the time of King Mongkut, and titles changed over successive reigns.
The rule about commoners also seems to be evolving, and it appears that there are no more restrictions on a commoner from becoming queen. Most of the titles below are from King Vajiravudh's 1924 enactment of the Succession Law.
Princes and princesses.
Holders of these titles are still considered royal, since they are (at most) two generations removed from a king. "Nai Luang" (ในหลวง) is an epithet for a king. Children of a king are called "Luk Luang" (ลูก หลวง "royal children"), and grandchildren of a king are called "Laan Luang" (หลาน "royal grandchildren"). The concept is similar to the French system of "princes of the blood" and the Iberian system of "infantes." In English, they are normally called "prince" or "princess". Special forms are used when one wishes to address them, although the language is less elaborate than when speaking to the king or the queen. A male Luk Luang who does not accede to the throne would assume a new royal surname, normally reflecting his birth name (as opposed to an honorific given later). The surname can be used by his wife if she is a commoner by birth, possibly with "Na Ayudhya" added if she has no noble title. It is otherwise not normally used until his children (or grandchildren) first hold the title of "Mom Chao", when the surname will first appear in their names.
Royal descendants.
More distant royal progeny, starting from the children of male Mom Chao, are considered commoners. However, these commoners have titles indicating that their ancestry can be traced back to a king.
Mom Rajawongse.
"Mom Rajawongse" (หม่อมราชวงศ์, ; abbreviated in Thai as ม.ร.ว. and in English as M. R. and translated as "His/Her Excellency") is the title assumed by children of male Mom Chao M.C.(English) M.C. After first name Informally, they may be called Khun Chai (male) or Khun Ying (female) (). Holders of this title are occasionally erroneously referred to as princes or princesses in older English documents; it is now more common to use the correct title, "Mom Rajawongse". If a specific title is appended, sometimes the titular may be called His/Her Grace by proclamation of the King or a Prince-Regent, but not by a Queen-regent or any royal member sitting in the King's capacity as a Councillor-of-State.
Mom Luang.
"Mom Luang" (หม่อมหลวง, abbreviated in Thai ม.ล. and sometimes in English as M. L. and translated as "The Honourable") are the last royal descendants retaining a title. Mom Luang titles are conferred on children of male Mom Rajawongse. Colloquially (although incorrectly), they are sometimes addressed as "Mom"; the correct informal address is "Khun" ().nlk
Na Ayudhya.
In the Family Name Act, B. E. 2465, Rama VI ordered that royal descendants who do not hold any title should append "Na Ayudhya" (ณ อยุธยา) to their surname to signify they are descended from a royal bloodline. Sometime spelled "Na Ayutthaya".
Wife of prince.
Wives of princes have titles, depending on the titles on both sides.
Phra Vorachaya.
"Phra Vorachaya" () is a title of the royal consort of the Crown Prince". She is elevated to "Phra Chao Vorawongse Ther Phra Ong Chao".
Phra Chaya.
"Phra Chaya" () is a princess, "Chao Fa" (HRH Princess) or "Phra Ong Chao" (HRH Princess) who is married to prince, at every level. She retains her own title. When referring to her as a wife of the prince, she may be called "Phra Chaya Nai (husband's name)".
Chaya.
"Chaya (ชายา)" is a princess or "Mom Chao" (HSH Princess) who is married to prince, at every level. Again, she would retain her own title. When referring to her as a wife of the prince, she may be called "Chaya Nai (husband's name)".
Mom.
"Mom (หม่อม)", in this context, is a commoner married to a prince. She uses this title as a prefix of her name, adding "na Ayudhya" to her new surname; for example, Mom Srirasmi Mahidol na Ayudhya (a wife of Chao Fa Maha Vajiralongkorn, whose surname is Mahidol). If she has her own title ("Mom Rajawongse" or "Mom Luang"), she retains it.
Married princesses.
The son of a holder of the following titles generally inherits a title one step below; a female Mom Rajawongse married to a commoner would produce a child with no title. According to the Royal Marriages Act, B. E. 2475, a princess wishing to marry to a commoner must request royal permission and abandon her royal title. For example, if princess Chao Fa, HRH Princess of Thailand, wished to marry a Mom Rajawongse commoner she would lose her royal title (Chao Fa, HRH Princess of Thailand) but retain royal style as follows: 
However, Chao Fa Chulabhorn Walailak received permission from the king to keep her title when she married commoner Virayudh Tishyasarin.
Royal peerage.
In addition to royal ranks and titles, royals may also receive noble titles in the style of the nobility. These are referred to as "krom" () titles. While the granting of noble titles ceased with the abolition of absolute monarchy in 1932, on very rare occasions the king may still grant an honorary noble title to a royal.
The noble title, which consists of a rank and a title, is appended to the royal name and title, prefixed with the word "krom" (pronounced "kromma" when forming part of the title). For example, the full title of the King's sister is "Somdej Phra Chao Pheenang Ther Chao Fa Galyani Vadhana "Kromma Luang Narathivat Rajanakarin". Nevertheless, it is the princely title which will be more frequently omitted when contracting the title "e.g." Somdej Phra Chao Boromawong Ther "Kromma Phraya Damrong Rajanubhab" (born Phra Ong Chao Disuankumaan). There are 5 feudal titles for prince/princess:
The ranks of royal peerage are:
Since the time of King Chulalongkorn, the honorific titles given to the royalties normally incorporate a city name or its modified form, and the holders are known in English as the Prince or Princess of that city.
The sovereign may grant titles to other royal-family members: 