Barbarous refers to the worst side of barbarian life, and to revolting acts, especially of cruelty, such as a civilized man would not be expected to do; as, a barbarous deed. We may, however, say barbarous nations, barbarous tribes, without implying anything more than want of civilization and culture.

J. C. Fernald, English Synonyms and Antonyms (1914)

Example sentences

cruel I think it is cruel to trap animals for fur coats.
brutal The city was ruined by the brutal force of nature.
savage There are still some savage tribes on that island.
inhuman At least I'm not starting to praise inhuman practices.
barbaric Algeria is a modern nation, not a barbaric country.
uncivilized There are still uncivilized lands.

Popularity over time

Word	1850 → 2019	Trend
barbarous		falling
cruel		rising
brutal		rising
savage		rising
inhuman		steady
barbaric		rising

Use in printed books, per decade from 1850 to 2019.

By length

4 letters: fell¹, wild¹, rude¹
5 letters: cruel², harsh¹, pagan²
6 letters: bloody², brutal², savage², fierce¹, gothic², vulgar², coarse¹, impure²
7 letters: strange¹, vicious², inhuman³, heathen², untamed, brutish², uncouth², wolfish
8 letters: ignorant³, ruthless², barbaric³, sadistic³, pitiless³, diabolic
9 letters: barbarian⁴, ferocious³, atrocious³, merciless³, roughshod², truculent³, untutored
10 letters: outlandish³, diabolical⁵, uncultured, sanguinary, unmerciful⁴, unlettered, flagitious
11 letters: uncivilized⁴, uncivilised
12 letters: uncultivated

The small number after each word is its number of syllables (cruel² = 2 syllables).