I’ve been looking at the use of the term ‘Tweed’ to describe the product of weaving.
There are no census references specifically to ‘Tweed’ weaving on Harris or Lewis prior to 1891.
The earliest that I’ve found elsewhere on the mainland is in 1861. The fact that the term originated (possibly due to a mis-transcription) in Scotland is well known.
What interests me is that it only appears on Harris and Lewis some three decades later. In 1889 the Scottish home Industries Association was formed to promote hand-crafted products, rather in the manner of John Ruskin’s Arts and Crafts Movement. Perhaps this goes some way to explain the widespread usage of the term ‘Tweed’ in the census returns for Harris just a couple of years later?
In 1891 & 1901 there were a total of 464 weavers of Tweed on Harris. They were overwhelmingly female. There were 15 weavers of Tweed on Lewis, only 3 of whom were female. This polarisation of Harris weaveresses and Lewis weavers continued through much of the 20th Century but I have yet to discover precisely why.
Wandering & Wondering 
In Janet Hunter’s book, it discusses this and she writes that it was due to the heaviness of the looms in Lewis, can’t quite remember why.