merciless (adjective) merciless: mean, heartless
Sinonime: acute,
central,
clamorous, climacteric, climatic,
compelling, deciding, decisive, desperate, dire,
essential, hanging by thread, high-priority,
imperative,
insistent, momentous,
necessary, on thin ice, pivotal, pressing,
searching, showdown, touch and go,
touchy, urgent, vital
Antonime: inessential, trivial, uncritical, unimportant