a man who has sexual intercourse with another male
This word is a coinage. It does not appear in any known Greek writing before Paul used it, and outside the New Testament it shows up first only in writers who depend on Paul. So its meaning cannot be settled by tracing how earlier Greek authors used it, because there is none to trace. Instead, the word is built out of two pieces lifted straight from the Greek Old Testament: the word for a male (ἄρρην, ἄρσην) and the word for a bed, which in Greek as in English stands for sexual relations. Those two pieces sit side by side in the Greek of Leviticus 18:22 and 20:13, the verses that forbid a man to lie with a male. The most widely accepted view is that Greek-speaking Jews welded those two words into one noun to name the man who does what Leviticus forbids. It is the Greek echo of a fixed Hebrew expression that meant the same thing.
Both times Paul uses the word he drops it into a list of behaviors that shut a person out of God's kingdom or that the law stands against. In Corinthians it comes right after a companion word (μαλακός), and many readers take the pair to name the two partners in male-male intercourse. The single steady meaning across both verses is a man who takes another male sexually.
What scholars still argue over is not whether the word is about male-male sex, but how wide its reach is: whether Paul meant every form of it or only the abusive and lopsided forms common in his world, such as a grown man with a boy or with a male prostitute. Those disagreements are recorded below; they are about the word's scope, not about replacing its core meaning with something else.