ויקרא פרק יט, יט וב ג ד כִלְאַיִם שַׁעַטְנֵּז לֹא יַעֲל ה עָל יך
מסכת נדה דף סא/ב שעטנז כתיב עד שיהיה שוע טווי ונוז
The Gemara understands the word שעטנז as a combination of three words שוע (combed) טווי (spun) and נוז (woven). There are many opinions in understanding the issur of wool and linen together.
Rashi explains that the violation occurs when all the operations (combed, spun and woven) are done to combine wool and linen, that the word יחדיו indicates all activities. Rabenu Tam explains the issur if any one of the actions occur (combed, spun or woven) to the wool or linen, and then the wool and linen are combined by a method of connection (יחדיו) such as a knot or weaving.
In general, in the Hebrew language words have a root of three letters. Thus, this word שעטנז, which has five letters, indicates the word is available for a word combination.
