1) Agelong 2) Constant 3) Endless 4) Eternal 5) Everlasting 6) Long 7) Never ending 8) Slow 9) Unlimited 1) Endless 2) Endless because of monotony 3) Eternal 4) French word used in English 5) Incapable of being terminated 6) Long 7) Seemingly without end 8) Tiresomely long 9) Unceasing 
• (a.) Without termination; admitting no limit; boundless; endless; wearisomely protracted; as, interminable space or duration; interminable sufferings.
In·ter'mi·na·ble adjective [ Latin interminabilis : confer French interminable . See Terminate .] Without termination; admitting no limit; boundless; endless; wearisomely protracted; as, interminable space or duration; interminable sufferings. « That wild 
interminable Without end; endless. Related 'together' units: com-; greg-; struct-. Cross references of word families related directly, or indirectly, to: 'internal organs, entrails, inside': ent-; enter-; fistul-; incret-; intra-; splanchn-; viscer-.
incapable of being terminated; unending: an interminable job. · monotonously or annoyingly protracted or continued; unceasing; incessant: I can't stand that interminable clatter. · having no limits: an interminable desert.
[SAT terms] tiresomely long; seemingly without end[Intelligent words] tiresomely long; seemingly without end