Correct spelling for the English word "Undull" is [ʌndˈʌl], [ʌndˈʌl], [ʌ_n_d_ˈʌ_l] (IPA phonetic alphabet).
The word "undull" is not found in most major dictionaries, and it does not have an established etymology. It appears to be a neologism, a newly coined word or phrase. The combination of "un-" as a prefix (meaning not) and "dull" (meaning boring or uninteresting) suggests that "undull" could be meant to convey the opposite of dullness, highlighting an absence of boredom or monotony. However, without more information on the specific context or origin of the word, it is difficult to determine its precise meaning or the intentions behind its creation.