A synonym for detrimental is harmful. Which is the best definition for detrimental

damaging is the answer

Straight off of google, Detrimental

tending to cause harm.

"releasing the documents would be detrimental to national security"

synonyms: harmful, damaging, injurious, hurtful, inimical, deleterious, destructive, ruinous, disastrous, bad, malign, adverse, undesirable, unfavorable, unfortunate;