[I'm going to try to start a series of posts for each Thursday, with each post talking briefly about a particular virtue or vice. I've long since found that I'm rather bad at keeping up extended series of posts, so no promises, and we'll see how long it lasts. But I do have a few things in the pipeline and also some things that can be revised and reposted, and the idea is that they'll usually be short summaries, so it might last a while before running out of steam.]
Yes, I made the word up; effeminacy is one of those vices that needs a new name. It's the usual English translation, but it has misleading associations. Malakia (which is one of the old Greek words for it, the other being anandreia, for which 'effeminacy' is a pretty straightforward translation) or mollience or mollity (which Anglicize the corresponding Latin, mollities, which is used in English occasionally as a medical term indicating abnormal softenss of an organ, but is not all that easy to pronounce) might work -- both mean 'softness' and have associations with the vice, although from what I understand the Greek word has come in modern Greek to have the sort of baggage (in this case, association with masturbation) that comes from being used as a vulgar insult. A new name is needed in part because 'effeminacy' suggests that only men can be effeminate, which is indeed how it has often been treated, but is obviously not true: Effeminacy considered as a vice is excessive avoidance of the difficult or painful. Thus Aristotle says in the Nicomachean Ethics (Book VII, section 7), "One who is deficient in resistance to pains that most men withstand with success, is malakos or luxurious, for luxury is a kind of malakia; such a man lets his cloak trail on the ground to escape the fatigue and trouble of lifting it, or feigns sickness, not seeing that to counterfeit misery is to be miserable." Aristotle also makes the interesting argument that, contrary to what is usually thought to be the case, excessive pursuit of amusements (for example, to the detriment of oneself or one's duties) really has more to do with avoiding pain than pursuing pleasure, properly speaking: amusement is a kind of rest from the pain of toil and labor, and so pursuit of amusement is (usually) more of a pursuit of rest from pain than a pursuit of pleasure itself. And that makes sense if you think about it; lots of amusements (slot machines, television) are obviously anodynes, and even amusements that are in some way difficult or tiring are usually pursued precisely because they are in some other way restful or relaxing.
Aquinas argues (ST 2-2.138.1) that effeminacy is opposed to the virtue of perseverance. He notes that nothing is considered soft if it yields to heavy blows (a wall is not soft if it can be broken by a battering ram), only if it yields to light ones, and so takes this to be the key feature of the vice. Since many of the motives that result in excessive yielding, like actual pleasure and fear of danger, are really pretty strong motivators, the motivation for real mollities has to be something that's generally pretty weak. On the basis of this he interprets Aristotle's account of vice in such a way as to come up with a full definition of the vice: withdrawal from good on account of sorrow caused by lack of pleasure, since mere dissatisfaction from not having pleasure is a comparatively weak motive, both psychologically and rationally. Someone who avoids a good solely because it doesn't give pleasure has a very weak reason for avoiding it, and is thus soft. The good in question is difficult only in the sense that it's not actively pleasant; it doesn't even need to be painful. That's a pretty low standard of difficulty.
With this refinement of Aristotle we get a good picture of just how common a vice mollities is: every act of avoiding something definitely good merely because it's not fun or enjoyable is an act associated with this vice.
Despite the fact that mollience is not confined to men, I think it's unsurprising that most words we have for it are words that are usually taken as insults for men; the virtue most associated with typical social ideas of masculinity is fortitude, and avoiding things that aren't fun is obviously a problem for fortitude (which requires perseverance).