noun, masculine/ˈluto/plural: lutos
mourning (feeling or expressing sorrow or regret, especially over someone's death)
“Estamos de luto.” — We're in mourning.
Synonyms: duelo
Related: de luto, enlutar, estar de luto
Probably a semi-learned borrowing from Latin lūctus, rather than an inheritance. A fully inherited form would be expected to be lucho.