The hours in each quarter (with the exception of the sixth hour in each quarter) are told with period-designating words or phrases, which are:[1] These terms are thought to have originated from the sounds of traditional timekeeping devices.
[2] Chao and bai translate as morning and afternoon respectively, and help to differentiate the two daytime quarters.
The sixth hour at dawn is called yam rung (ย่ำรุ่ง, [jâm rûŋ]), and the sixth hour at dusk is called yam kham (ย่ำค่ำ, [jâm kʰâm]), both references to the act of striking the gong or drum in succession to announce the turning of day (yam), where rung and kham, meaning dawn and dusk, denote the time of these occurrences.
[1] Midnight is also called song yam (สองยาม, [sɔ̌ːŋ jāːm]; note that yam is a different word), a reference to the end of the second three-hour period of the night watch (song translates as the number two).
In addition, hok (6) thum and ti hok may also be used to refer to the hours of midnight and dawn, following general usage for the other hours, although more rarely; and the fourth to sixth hours of the second daytime half may also be told as ...mong yen (...โมงเย็น, [mōːŋ jēn]), yen meaning evening.