WordNet sense 1 (tiresomely long; seemingly without end):

eternal, interminable

WordNet sense 2 (primarily temporal sense; being or indicating a relatively great or greater than average duration or passage of time or a duration as specified):

long

WordNet sense 3 (having no known beginning and presumably no end):

dateless, sempiternal

WordNet sense 4 (having no limits or boundaries in time or space or extent or magnitude):

infinite

WordNet sense 5 (continuing in time or space without interruption):

continuous, uninterrupted

WordNet sense 6 (occurring so frequently as to seem ceaseless or uninterrupted):

incessant, perpetual

WordNet sense 7 (seemingly without interruption; chiefly restricted to what recurs regularly or frequently in a prolonged and closely spaced series):

continual