Forgive me, but I see no 100% semantic equivalent between the Hebrew and the Greek for "sin offering." It is rare that a single religious word has complete semantic equivalence with a single word in another language. In this case, the LXX translators did not necessarily mean complete semantic equivalent between the Hebrew and Greek, but simply used what they thought was the best Greek word they had. Example: the one English (or Greek) word "justify" in the Japanese Bible must be three words, gi to mitomeru (義と認める).
Look at Hebrews 10:18, where we have προσφορὰ περὶ ἁμαρτίας, three words to say "offering for sin," including separate words for "offering" and "for" and "sin." In fact, back in Hebrews 10:8 we have ὁλοκαυτώματα (accusative) for "burnt offering," then following that περὶ ἁμαρτίας, indicating another offering, a sin offering, following the context of a burnt offering, and using two words for "sin offering" with "offering" being in italics in the KJV.
In Hebrew, on the other hand, there are separate words for "sin offering" (חטּאה) and just "offering" (מנחה), and that is different from Greek.