How Do You Spell UNDERLIED?
Pronunciation: [ˌʌndəlˈa͡ɪd] (IPA) 
The word "underlied" is spelled in a way that may be confusing to some. It is pronounced as /ʌndərˈlaɪd/ using IPA phonetic transcription. The root word is "underlie," but the additional "d" at the end of "lied" changes the tense to past tense or a completed action. The spelling with the extra "d" may look incorrect, but it's a standard and acceptable way to spell the past participle of "underlie."
