Antonyms of adj nightmarish

1 sense of nightmarish

Sense 1
bloodcurdling, hair-raising, nightmarish -- (extremely alarming)

INDIRECT (VIA alarming) -> unalarming -- (not alarming; assuaging alarm)

Similarity of adj nightmarish

1 sense of nightmarish

Sense 1
bloodcurdling, hair-raising, nightmarish -- (extremely alarming)
       => alarming (vs. unalarming) -- (frightening because of an awareness of danger)