I asked on the Reddit about why Desempenhar wasn’t the opposite of Empenhar. Empenhar means “to make an effort”, and the prefix “des” is like “dis” in english and it usually reverses or negates the meaning of whatever word it’s attached to and makes it into an antonym. So for example, “Fazer” means to make or do, and “Desfazer” mean to take something apart; “Cansar” means to get tired, “Descansar” means to rest, “Ordem” means “Order” and “Desordem” means “Disorder” and so on. So desempenhar looks like it should mean “make no effort” (“Hoje é dia de folga, pá. Vou me desempenhar o dia inteiro!”) but it doesn’t, it means “to perform”.
Why? Is there some sort of mysterious etymological tale to tell here? Same question for their noun forms, empenho (effort) and desempenho (performance).
As it turns out, it’s just one of those things like Flammable and Inflammable in english, where the prefix just doesn’t really have any effect. A few interesting points came up in the comments
Butt_Roidholds listed some other examples of this sort of thing:
- Abrir = open / Desabrir means leave off doing something… hm… I’m not absolutely sure about this one. Abrir can mean “Open the proceedings” – ie, start something, so desabrir meaning cease doing something actually does seem to be an antonym
- Obstinado = obstinate / Desobstinado = something like “disoriented” but it’s not very clear – it isn’t defined in Priberam and Infopedia just says “ver desaustinado”. It seems like an odd fish and I won’t be using it!
- Inquieto = disquieted / Desinquieto = exactly the same as inquieto! Why does this even exist though? They already have the word “quieto”, so why the double negative?
- Aliviar = alleviate / desaliviar = alleviate.
And other users, TheSingingBowl and Vilkav chimed in with
- Abrochar = to fasten with a brooch, or to button up / Desabrochar = open or unbutton, can also refer to the opening of a flower. These seem like pretty decent antonyms but the person who suggested them added a laughing emoji so I think it might have to do with the other (rude) meaning of “broche”.
- Largar = let go / Deslargar = let go. Yep, definite example.
As for theories about how the words got like this, the most interesting one was from Grenarius who suggested maybe Desempenho came from the word “penhor” which is like “pawn” in the sense of something given as security for a high interest loan, and when you would “se empenhar” you were incurring an obligation which you would then discharge, so desempenha is an antonym of “se empenha” in that sense: you are performing some work to pay off your debt. It’s a minor stretch but not out of the realms of possibility