La mayoría de estas palabras terminan en "-io" ...
The majority of these Spanish words end with "-io"
- so (for me, at least) distinguishing "-io" from "-ío" is not as difficult as trying to remember which nouns take "-ía" -

It would be impractical to list more than just a tiny sample, e.g.
adverbio, ejercicio, beneficio, edificio, juicio, servicio, silencio, subsidio, radio, medio, epitafio, sacrilegio, prestigio, auxilio, premio, genio, principio, diario, vocabulario, adversario, imperio, criterio, misterio, gimnasio, patio, novio ...

However, there are some important exceptions in "-ío" (but not too many to learn):

desafío .. challenge, competition, rivalry
desvío ... detour
envío ... dispatch, shipment
judío ... Jew
navío ... ship
rocío ... dew
sombrío ... shaded, gloomy, sad
tardío ... late, overdue
vacío ... empty
 

No hay ningún sustantivo ni adjetivo monosilábico en español con esta pauta ...
It is also worth remembering that there are no monosyllabic Spanish nouns or adjectives of this nature (i.e., none which are similar to the third person past tense forms "dio" and "vio") ... so we have

brío ... spirit, verve, determination
crío ... child, brat
frío ... cold - and of course derivatives like "resfrío" (a 'cold' - i.e. an infection)
lío ... bundle, confusion, liaison
mío ... mine
pío ... pious - so the opposite, i.e. "impío" is included
río ... river
tío ... uncle
trío ... trio
 
 

Some less common words in "-ío":

"-erío" is often a suffix denoting "a group of ..." -

caserío ... hamlet, cluster of houses or buildings
facherío ... group of fascists
graderío ... terrace, flight of steps
griterío ... shouting, uproar, cacophony of loud voices
guaperío ... group of famous or well-to-do people
mocerío ... crowd of young people
mujerío ... gathering of women
pijerío ... group of snobs
rojerío ... group of leftists
vocerío ... shouting, uproar, cacophony of loud voices
with which we can also mention:
cabrío ... herd of goats; also an adjective: goatish
gentío ... crowd, throng
 

Suffixes "-dío" and "-tío" are sometimes found with nouns denoting types of land:

baldío ... useless terrain
labradío & labrantío ... arable land
plantío ... plots ready for planting, or which already contain plants
sembradío ... land ready for sowing
regadío ...  plots which require irrigation
 

Here are a few other Spanish words with "-ío" -

albedrío ... free will, whim
amorío ... love affair
atavío ... attire dress
avío ... use, preparation, provision
bajío ... sandbank, shoal
baldío ... in vain
bohío, buhío ... hut, shack (Latin American)
chuchurrío ... wilted
descarrío ... process of going astray
desvarío ... delirium
estío ... summertime
extravío ... loss, straying
hastío ... weariness, boredom
jipío ... flamenco lament
montepío ... charitable society, pawnshop
poderío ... power, authority
puterío ... prostitution
señorío ... domain, dominion
trapío ... grace, charm
tronío ... extravagance

David L. McNaughton

Correo electrónico: DLMcN@yahoo.com

Sustantivos con terminaciones en “-ía” en lugar de “-ia” ... http://DLMcN.com/iawords.doc

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