【Brutal】 , 【brute】 , 【brutish】 , 【bestial】 , 【beastly】 , 【feral】 are not close synonyms, though all suggest a likeness to or the nature of a lower animal and all, especially as applied to persons, tend to express strong derogation.

【Brutal】 is almost exclusively applied to men or their acts, characters, or words; it implies qualities (as sensuality, lack of intelligence or feeling, or inhumanity) that relate them to the lower animals.

【Brute】 is sometimes employed in distinguishing an animal from a man, but more often it applies to something inanimate that can be likened to the lower animals (as in its soullessness, its irrationality, its blindness, its immobility, or its inflexibility).

【Brutish】 , like 【brutal】 , is usually applied to men or their acts, their minds, and their passions; it differs from 【brutal】 in that it rarely suggests cruelty and inhumanity but stresses likeness to an animal in stupidity, in lack of control over appetites, or in government by instinct.

【Bestial】 likewise applies to men and their acts, their minds, and their manners, but it usually stresses neither inhumanity nor a low-grade mind but a depravity or state of degradation unworthy of man and fit only for beasts and is therefore usually a term of severe reprobation.

【Beastly】 may come close to 【bestial】  in its suggestion of utter depravity or abominable character, but more often it is weakened and implies no more than disapprobation of something unpleasant or distasteful to a greater or less degree.

【Feral】 , when applied to men, suggests savagery or ferocity.