A word glossed “for ever” in the phrase ar i Eru i or ilyë mahalmar ëa tennoio “and of the One who is above all thrones for ever” (UT/305). It is a combination of tenna “until” and oi(o) “ever”, so perhaps more literally “until eternity” = “*forevermore”. As such I think this word specifically implies “from now until the end of time” but not necessarily forever in the past, as opposed to oialë which can be used to mean “forever” both forwards and backwards in time.