what does the word "tatheer" [تطہیر] mean?

Re: what does the word “tatheer” تطہیر] mean?

thik say yaad nahi, magar wo shaid kisi challenge/ mubahala say mutaliq hay, where a christian delegation came to Madina tuNabi S.A.W. and argued about Hazrat Isa A.S. baqi google karlain : p