on or near a border or boundary.

uncertain; indeterminate; debatable

not an alcoholic, but a borderline case.

not quite meeting accepted, expected, or average standards.

approaching bad taste or obscenity

He made several borderline remarks that offended them.

a person suffering from borderline personality.

adjective

certain , definite , exact , sure

adjective

ambiguous , ambivalent , doubtful , dubitable , equivocal , indecisive , indefinite , indeterminate , marginal , open , problematic , uncertain , unclassifiable , unclear , undecided , unsettled , chancy , clouded , dubious , inconclusive , problematical , questionable , unsure , controversial , debatable , inexact , intermediate , liminal , peripheral , skeptical , suspicious , vague , verge

noun

brim , brink , edge , edging , fringe , margin , periphery , rim , verge , point , threshold