Adjectives ending with the letter O are listed in this post.
accelerando, adagio, agitato, ago, akimbo, allegretto, allegro, amido, amino, andantino, audio
bamboo, barocco
calando, calico
deco, decrescendo, de-facto, doloroso, duodecimo
eighteenmo, embryo, espressivo, eurasiatio
fifty-two, folio, fugato
giusto, go-go, gustoso
imido, improviso, incognito, indigo, infinito
jalapeno, jumbo
kimbo
lacrimoso, larghetto, largo, latino, lean-to, legato, lentando, lento
macho, maestoso, mantchoo, marcato, merino, mezzo, mezzo-soprano, micro, misurato, moderato, morendo, morisco, muscovado
obligato, octavo, octodecimo, one-two, oo
piano, pieno, pinto, pomposo, primo, puerto
quarto
rallentando, retro, rinforzando, ripieno, ritardando, ritenuto, rococo, rubato
secco, sfumato, sgraffito, so-so, sostenuto, spiccato, spiritoso, squintifego, staccato, stringendo, subzero
tardo, techno, telephoto, thoro, tosto, tremando, tremolando, trigesimo-secundo, twelvemo, twenty-fourmo, two
unco, uptempo
video, vigesimo-quarto, vigoroso, virtuoso, vittorio, voodoo
well-to-do
year-ago
Hope this word list had the adjective that ends in O you were looking for. Additional descriptive words can be found in the other pages on this site.
Please add more adjectives to make this list more complete: