Pronunciation: [hˈadst pˈɑːt ˈɪn] (IPA) 
The spelling "hadst part in" is an archaic form of "had a part in" and is seen in older literature. The pronunciation of "had" is the same as in the modern version, but "part" is pronounced as "pɑːt" instead of "pɑːrt". The "-st" at the end of "hadst" indicates the second person singular past tense form of "have". The IPA phonetic transcription of "hadst part in" is /hædst pɑːt ɪn/.
"Hadst part in" is an archaic term derived from Old English, specifically the second-person singular past tense form of "have" and the word "part." It refers to having a share, involvement, or participation in something, typically something significant or noteworthy.
The term "hadst" is the combination of "had" and "thou," indicating that the action or possession occurred in the past and was specifically directed towards the second person singular pronoun, "thou." In this context, "thou" is an obsolete form of "you."
The word "part" in this phrase refers to a role, portion, or division of something. It refers to an individual's involvement or contribution to a particular event, undertaking, or situation.
When combined, "hadst part in" expresses the act of having or owning a portion or role in an event or situation that has already occurred, specifically addressing the thou-form in English. It implies that the individual played a significant role or had a notable share in the said event.
Overall, "hadst part in" signifies having been actively engaged or having contributed significantly in the past, emphasizing the significance and direct involvement of the second-person singular in the given context. This phrase is now considered archaic and is rarely used in modern English.
