26 For this cause God gave them up unto vile affections: for even their women did change the natural use into that which is against nature:
27 and likewise also the men, leaving the natural use of the woman, burned in their lust one toward another; men with men working that which is unseemly, and receiving in themselves that recompence of their error which was meet."
In these two passages, Paul (or whoever wrote this epistle) used the word arsenokoites. A word that hasn't been found in any earlier Greek texts, it appears to have been formed by merging two words, arsen - male and koites - bed. There were other Greek words used at the time with meanings closer to what we call homosexual or gay. The question asked by scholars: Why did the writer make up a new word when others existed?
In context, from what is known about cultic practices in the Greco-Roman culture of the 1st century, it is likely that Paul was condemning either temple prostitution or the forced sexual exploitation of slaves by their owners or pederasty.
The other word found in Romans and in Corinthians is malakos which has a basic meaning of "soft" or "dainty" but was also used in other Greek texts to mean effeminate or weak men, not necessarily gay.