Welsher is a slur used to describe Welsh in a derogatory way. Supposedly dates from the 19th Century when the English government decided that all Welsh children should speak English in school. Any child caught speaking Welsh had a board placed around his/her neck and could only get rid of it by "telling on" another
The word Welsher is a racial slur that has been used historically to degrade and dehumanize welsh. The word is still used by some people for this purpose, and it is seen as offensive and hurtful to welsh. If you are unsure about whether or not it is appropriate to use the word Welsher, it is best to err on the side of caution and avoid using it in any situation.