Fierce, truculent, ferocious, barbarous, savage, inhuman, cruel, fell are comparable when they mean displaying fury or malignity in looks or in actions.
Fierce is applied to men or to animals that inspire terror because of their menacing aspect or their unrestrained fury in attack.
Truculent, though it implies fierceness, especially of aspect, suggests the intent to inspire terror or to threaten rather than the achievement of that intention. Consequently it often implies a bullying attitude or pose. It is applied chiefly to persons, groups of persons, and nations.
Ferocious not only connotes extreme fierceness but it implies actions suggestive of a wild beast on a rampage or in an attack on its prey; it therefore usually implies unrestrained violence, extreme fury, and wanton brutality.
Barbarous (see also BARBARIAN ) in its extended sense applies only to civilized persons or their actions; it implies a harshness, a brutality, and, often, a ferocity thought of as unworthy of human beings in an advanced state of culture.
Savage (see also BARBARIAN ) implies an absence of the restraints imposed by civilization or of the inhibitions characteristic of civilized man when dealing with those whom he hates or fears or when filled with rage, lust, or other violent passion.
Inhuman is even stronger than savage, for it suggests not so much undue violence or lack of restraint as absence of all feeling that normally characterizes a human being: on the one hand it may suggest wanton brutality, or on the other hand it may imply absence of all capacity for love, kindness, or pity.
Cruel implies indifference to the suffering of others and even a positive pleasure in witnessing it or in inflicting it.
Fell, which is chiefly rhetorical or poetic, connotes dire or baleful cruelty.