"careful to avoid danger or misfortune," 1640s, from caution + -ous. The Latin word for this was cautus "careful, heedful." Related: Cautiously; cautiousness.
Entries linking to cautious
caution n.
c. 1300, caucioun, "bail, guarantee, pledge," from Old French caution "security, surety" (13c.), from Latin cautionem (nominative cautio) "caution, care, foresight, precaution," noun of action from past-participle stem of cavere "to be on one's guard" (from PIE root *keu- "to see, observe, perceive").
The Latin sense re-emerged in English as "prudence in regard to danger" (1650s). The meaning "word of warning, monitory advice" is from c. 1600. The meaning "anything which excites alarm or astonishment" is U.S. slang, 1835.
-ous
word-forming element making adjectives from nouns, meaning "having, full of, having to do with, doing, inclined to," from Old French -ous, -eux, from Latin -osus (compare -ose (1)). In chemistry, "having a lower valence than forms expressed in -ic."