Vote #1 Colin Jensen and Joe Fessenden, who have nailed it.
To add a bit.
It is the height of arrogance to fast forward to Modern Greek. But I’ll do so anyway.
In Modern Greek, the adjective askhimos < askhēmōn means ‘ugly’.
The etymology of askhēmōn is ‘un-shape-ish’. So unshapely, not with a nice shape. Deformed, as Thayer’s Lexicon put it. Not pleasant to look at.
The verb askhēmonein means ‘to act in an unshapely manner’. To act ugly. In a way that is not pleasant to experience.
You need to dig beneath the Olde English of unbecomingly, unseemly. They are correct, but you may well miss the connotations because they are Olde English. To act unbecomingly mean acting in a socially unacceptable way. It is a socially ugly way.
From the Byzantine usage I’ve seen, I’m pretty sure that includes behaviour which society (at the time) condemned as lewd, sexually ill-disciplined. But it’s not just about the sex, it’s about the ugliness.
FWIW, the LSJ (Classical Greek) definition of the verb is ‘behave unseemly, disgrace oneself’.