gallero
cockfighter
gallo
rooster
+
-ero
person who does something (profession)
Gallero means cockfighter and can be broken down into gallo0 (rooster0) + -ero1 (person who does something1), literally meaning 'a person who works with roosters'.
noun
- cockfighterA person who breeds or trains roosters for cockfightingEl gallero pasaba horas entrenando a sus gallos de pelea. // The cockfighter spent hours training his fighting roosters.