Correct spelling for the English word "letted know" is [lˈɛtɪd nˈə͡ʊ], [lˈɛtɪd nˈəʊ], [l_ˈɛ_t_ɪ_d n_ˈəʊ] (IPA phonetic alphabet).
The phrase "letted know" is actually a combination of two words: "let" and "know".
The word "let" comes from the Old English word "lǣtan", which means "to permit" or "to allow". This term has roots in Old High German ("lazzen") and Middle Dutch ("lāten"). Over time, "let" has taken on various meanings, including hindering or delaying, as well as allowing or permitting.
The word "know" originates from the Old English word "cnāwan", which means "to recognize" or "to perceive". This term is related to the Old Norse word "kenna" and the German word "kennen".
When combined, "letted know" indicates the act of allowing or permitting someone to be aware of something or sharing information with them.