The Cambodian script (called Khmer letters) are all probably derived from various forms of the ancient Brahmi script of South India. The Cambodian script has symbols for thirty-three consonants, twenty-four dependent vowels, twelve independent vowels, and several diacritic symbols. Most consonants have reduced or modified forms, called sub-consonants, when they occur as the second member of a consonant cluster. Vowels may be written before, after, over, or under a consonant symbol.
Some efforts to standardize Khmer spelling have been attempted, but inconsistencies persist, and many words have more than one accepted spelling. A two-volume dictionary prepared under the direction of the Venerable Chuon Nath of the Buddhist Institute in Phnom Penh is the standard work on Khmer lexicography.
Khmer is divided into three historical stages: Old Khmer (seventh to twelfth century A.D.), Middle Khmer (twelfth to seventeenth century A.D.), and Modern Khmer (seventeenth century to the present). It is likely that Old Khmer was the language of Chenla. The language of Funan was most probably a Mon-Khmer language. The earliest inscription in Khmer, found at Angkor Borei in Takev Province south of Phnom Penh, dates from A.D. 611.