Real Dictionary

thread
countable noun: The thread of an argument, a story, or a situation is an aspect of it that connects all the different parts together.
variable noun: Thread or a thread is a long very thin piece of a material such as cotton, nylon, or silk, especially one that is used in sewing.

thread in American English
a light, fine, stringlike length of material made up of two or more fibers or strands of spun cotton, flax, silk, etc. twisted together and used in sewing
noun: a fine cord of flax, cotton, or other fibrous material spun out to considerable length, esp. when composed of two or more filaments twisted together

thread in British English
noun: a fine strand, filament or fibre of some material
verb: to pass (thread, film, magnetic tape, etc) through (something)

thread in Mechanical Engineering
noun: A thread is a helical-shaped groove cut in a cylindrical hole (the female thread), or a helical-shaped ridge on a cylindrical bar, rod, shank, etc (the male thread).