Suo is a kind of Japanese kimono. Menswear.
Since the Kamakura period, hitatare had become a full-dress. Among them, simple and classical style hitatare were called suo in the Muromachi period. Although it was lower ranked samurai's casual wear in the beginning, it became the second most formal dress after daimon (crested formal robe) in the end of the Muromachi period. The largest difference is that hitatare and daimon used a white waist cord while the suo's cord was made with the same cloth. Moreover, strings that pierce around the sleeves and thin cloth around the armhole were omitted, and the breast cord and the ornament cord (decoration strings of sleeves or a breast) were made from leather. Therefore, it is also called 'hitatare of kawao' (leather cord). A koshiita (back plate) had been added to the back side of hakama (divided skirt) since the end of the Muromachi period. It might be made with various colors and patterns.
In the Edo period, it was determined as a formal dress for a samurai ranked Ikai (court rank) below Rokui (Sixth Rank) by the feudal government. During the Edo period, suo became full dress of hatamoto (a direct vassal of the shogun) because hatamoto was ranked below Ikai.
Its material was limited to bleached cotton, and Kamon (family crest) was put on eight places in total, back, chests, sleeves, koshiita and both sides of slacks side seam of hakama. Usually, hakama was very long and trailed.
When 'hanbakama,' an ankle length hakama, which was not used with hitatare or daimon, was worn, it was called 'kosuo.'
Nowadays, suo may be worn by a minister at rites and festivals. Moreover, simplified suo may be used as a costume in Noh plays and kyogen.
In 'Suo Otoshi' of kyogen, suo plays a major role.