That does not relent, incapable of relenting (in various senses); spec. (in early use) harsh or inflexible, unyielding; (now usually) that does not…

Not reduced in intensity or severity; not softened (in feeling, brightness, harshness, etc.); unrelieved.

Without reference to consciously directed effort: not diminishing in intensity or severity; unabating, unremitting; (later also) unvarying…

(un-, prefix1 affix 2.)

Of a sword, lance, etc.: not blunted or dulled; sharp. Formerly also figurative and in extended use. Now chiefly historical.

(un-, prefix1 affix 2.)

Not made lighter or less weighty. Also figurative: unalleviated; unrelieved.