-ious

suffix forming adjectives meaning 'characterized by, full of', often corresponding to nouns in -ion (cautious; curious; spacious).
Etymology: from or after F -ieux f. L -iosus

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adjective suffix

Etymology: Middle English, partly from Old French -ious, -ios, -ieus, -ieux, from Latin -iosus, from -i- (penultimate vowel in nouns such as religio religion, malitia malice, species species, appearance, spatium space) + -osus -ose, and partly from Latin -ius (final portion of the nominative singular masculine form of adjectives such as meritorius that brings in money)

: -ous

edacious

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variant of -ous, added to stems of Latin origin, often with corresponding nouns ending in -ity: atrocious; hilarious. Cf. -eous.

[ME \<\< L -iosus (see -I-, -OSE¹) and L -ius (masc. sing. adj. ending, as in varius)]

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suffix (forming adjectives) characterized by; full of

cautious | vivacious

Origin:

from French -ieux, from Latin -iosus

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-ious

a compound suffix, consisting of the suffix -ous, added to an i which is part of another suffix, repr. L. -iōsus, F. -ieux, with sense ‘characterized by, full of’. Found in L. in adjs. formed from derivative ns. in -ia, -ies, -ius, -ium, as invidiōsus invidious, perniciōsus pernicious, ēbriōsus drunken, ebrious, odiōsus odious; by false analogy in cūriōsus curious (from cūra): see -ous. Also in adjs. belonging to ns. in -io, -iōn-em, as ambit-iōs-us (from ambit-iōn-em) ambitious; so captiōsus captious, factiōsus factious, obliviōsus oblivious, religiōsus scrupulous, religious, seditiōsus seditious, suspiciōsus suspicious, etc. By analogical extension from these, there is a tendency in English to form an adj. in -ious beside any n. in -ion, esp. those in -tion, -cion, -sion, e.g. rebell-ion, -ious, caution, -ious, infection, -ious, contradictious, deceptious, disputatious, dissentious (for -sious), ignitious. Adjs. in -ious are also formed in Eng. by adding -ous to the stem of L. adjs. in -i-us, e.g. L. vari-us various; also in -itious from L. -īci-us, as adventitious: see -itious, and -ous.