The spelling of the word "hadst sex" follows the Old English language rules. The word "hadst" is the second person singular past tense of the verb "have" in the subjunctive mood. The IPA phonetic transcription of "hadst" is /hædst/. The word "sex" is derived from the Latin word "sexus" and its meaning has not changed over time. The IPA phonetic transcription of "sex" is /sɛks/. Together, "hadst sex" would mean "if you had sex" in Old English.