This is the 12654th most frequent Spanish word.
nadadora
"Swimmer" (female).
Here, 'nadadora' refers to a female swimmer, showing its use as a noun.
La nadadora ganó la competencia de natación.
The swimmer won the swimming competition.
In this case, 'nadadora' is also a noun but used here in an appositive phrase to describe the girl.
Esa chica, una gran nadadora, entrena todos los días.
That girl, a great swimmer, trains every day.
Again, 'nadadora' functions as a noun describing the subject, emphasizing skills.