This is the 4056th most frequent Spanish word.
culebro
Culebro: A large snake or serpent.
Here, 'culebro' refers to a large snake, using the word to emphasize its magnitude or prominence.
Vi un culebro enorme en el río.
I saw a huge snake in the river.
In this sentence, 'culebro' is used metaphorically to describe a complicated or convoluted situation.
El problema se ha convertido en todo un culebro.
The problem has turned into a real mess.
This usage of 'culebro' is literal, referring to a specific snake believed to inhabit the cave.