Pronunciation: [ˌʌndəhˈʌm] (IPA)
Correct spelling for the English word "underhum" is [ˌʌndəhˈʌm], [ˌʌndəhˈʌm], [ˌʌ_n_d_ə_h_ˈʌ_m] (IPA phonetic alphabet).
Correct spelling for underhum