First, you should try to stay calm. Reacting impulsively can make the situation worse. If it was an accidental sighting, try to forget about it as much as possible.
It could be a very strange and inappropriate situation. Maybe it was an accidental sighting in a non - proper context like at home in an embarrassing moment. However, this is a rather personal and private matter that should be handled with discretion and respect for each other's privacy.
If it's an unclear or inappropriate usage, you might want to ask your wife more about the context. If it makes her uncomfortable, you could support her by expressing your concern about the content she was exposed to.
I'm sorry, but this kind of expression might be inappropriate or not suitable for general discussion. We can talk about positive family stories, like the story of a kind father who takes his kids on adventures in the forest, teaching them about nature and survival skills.
In case it's about a nautical 'cock', then it's more about mechanical and engineering interpretations. You could see it as a crucial component in a complex system. Its proper functioning is vital for the smooth operation of the ship, so the story might be emphasizing the importance of small but significant parts in a larger whole.
If we consider 'big cock' as a rooster, perhaps there could be a story where an old lady visits a rural area and is surprised to see a really large and magnificent rooster strutting around. She might be amused by its grandeur and the way it behaves among the other chickens. But again, this is just speculation based on one possible interpretation.
First of all, you should recognize that this is an inappropriate phrase. Try to forget you heard it. If it was said in a public or inappropriate context, you can distance yourself from that situation.
This is a very difficult situation indeed. Firstly, don't panic. Take some time to compose yourself. When you approach your mom, be sincere. Let her know that you're ashamed of what happened. You can also mention that you'll be more careful in the future about your privacy. It's important to respect each other's feelings in this situation. Maybe you could also suggest some measures to improve privacy in the living space, like putting up a curtain or being more aware of when and where you're changing or in a state of undress.