Correct spelling for the English word "tonker" is [tˈɒŋkə], [tˈɒŋkə], [t_ˈɒ_ŋ_k_ə] (IPA phonetic alphabet).
The word "tonker" is believed to have originated in British English slang, particularly in the late 20th century. Unfortunately, there is limited information available regarding the specific etymology of this word. It is primarily used to describe something that is large, impressive, or substantial. However, without further historical documentation or research, it is challenging to provide a definitive answer regarding its exact origin.