Plural

-a, -e/-é, -i, -o, -u + -s

casa, monte, café, taxi, oso, espíritu
casas, montes, cafés, taxis, osos, espíritus

casa amarilla, taxi rojo, oso pequeño
casas amarillas, taxis rojos, osos pequeños

house, mount, coffee, take, bear, spirit
houses, mounts, coffees, takes, bears, spirits

yellow house, red taxi, little bear
yellow houses, red taxis, little bears

stressed -a, -o + -s

papá, dominó
papás, dominós

dad, dominoes
dads, dominoes

stressed -i, -u + -s

colibrí, tabú
colibrís/colibríes, tabús/tabúes

hummingbird, taboo
hummingbirds, taboos

-y + -es

rey, convoy, buey
reyes, convoyes, bueyes

king, convoy, ox
kings, convoys, oxen

foreign words -y English > -i + -s

ferry Eng. > ferri (singular) > ferris (plural)
dandy Eng. > dandi (singular) > dandis (plural)

-s, -x + -es

compás, danés, vals
compases, daneses, valses

compass, Danish, waltz
compasses, the Danish, waltzes

-l, -r, -n, -z, -d, -j, -s, -x, -ch + -es

baúl, escritor, delfín, mitad, voz
baúles, escritores, delfines, mitades, voces

reloj, ciprés
relojes, cipreses

chest, writer, dolphin, voice, watch
chests, writers, dolphins, voices, watches

watch, cypress
watches, cypresses

-ch + -es

sándwich
sándwiches

sandwich
sandwiches