Wikipedia
Chokutō
The is a straight, one-edged Japanese sword that was produced prior to the 10th century. Its basic style is likely derived from similar swords of ancient China. Chokutō were used on foot for stabbing or slashing and were worn hung from the waist.The Japanese sword, Kanzan Satō, Kodansha International, May 30, 1983 P.28
"Katana:The Samurai Sword",Stephen Turnbull,2010,P.16 Until the Heian period such swords were called , which should not be confused with tachi written as referring to curved swords.