Without compunction or human feeling:
— Cold-blooded killing.

synonyms: cold, inhuman, insensate.

Roget 826: inexcitable^†, unexcitable; imperturbable; unsusceptible etc. (insensible) 823; unpassionate^†, dispassionate; cold-blooded, irritable; enduring etc. v.; stoical, Platonic, philosophic, staid, stayed; sober, sober minded; grave; sober as a judge, grave as a judge; sedate, demure, cool-headed.    easy-going, peaceful, placid, calm; quiet as a mouse; tranquil, serene; cool as a cucumber, cool as a custard; undemonstrative.    temperate etc. (moderate) 174; composed, collected; unexcited, unstirred, unruffled, undisturbed, unperturbed, unimpassioned; unoffended^†; unresisting.    meek, tolerant; patient, patient as Job; submissive etc. 725; tame; content, resigned, chastened, subdued, lamblike^†; gentle as a lamb; suaviter in modo [Lat.]; mild as mothers milk; soft as peppermint; armed with patience, bearing with, clement, long-suffering.    ... show more

Roget 907: malevolent, unbenevolent; unbenign; ill-disposed, ill-intentioned, ill-natured, ill-conditioned, ill-contrived; evil-minded, evil-disposed; black-browed^†.    malicious; malign, malignant; rancorous; despiteful, spiteful; mordacious, caustic, bitter, envenomed, acrimonious, virulent; unamiable, uncharitable; maleficent, venomous, grinding, galling.    harsh, disobliging; unkind, unfriendly, ungracious; inofficious^†; invidious; uncandid; churlish etc. (discourteous) 895; surly, sullen etc. 901.1. cold, cold-blooded, cold-hearted; black-hearted, hard-hearted, flint-hearted, marble-hearted, stony-hearted; hard of heart, unnatural; ruthless etc. (unmerciful) 914.1; relentless etc. (revengeful) 919.    cruel; brutal, brutish; savage, savage as a bear, savage as a tiger; ferine^†, ferocious; inhuman; barbarous, barbaric, semibarbaric, fell, untamed, tameless, truculent, incendiary; bloodthirsty etc. (murderous) 361; atrocious; bloodyminded^†.    fiendish, fiendlike^†; demoniacal; diabolic, diabolical; devilish, infernal, hellish, Satanic; Tartaran.    ... show more

Having cold blood (in animals whose body temperature is not internally regulated).