The word "bastardies" is spelled with a "t" in the middle, despite the fact that it is pronounced with a "d" sound. This discrepancy is due to a phenomenon known as voicing assimilation. In English, when two consonants are in close proximity, the second consonant often takes on the voicing of the first one. In this case, the "t" is pronounced as a "d" because it follows the voiced consonant "r". So, despite the unusual spelling, "bastardies" is pronounced /ˈbæstərdiz/.
The word "bastardies" is the plural form of the noun "bastardy". The etymology of "bastardy" derives from the Middle English word "basterde", which originated from Old French "bastart", ultimately derived from Late Latin "bastardus". In turn, Late Latin borrowed the term from the Latin "bastum", meaning "packsaddle". The shift in meaning from "packsaddle" to "illegitimate child" likely occurred due to the association of a packsaddle with a horse of mixed breed. Over time, the term "bastard" came to refer to a child born out of wedlock or with unknown paternity.