decline, ebbing, go down, attenuation, dwindling, tail-off, fading, dwindlement, diminution, diminishing, more...

wax, increase, intensify, strengthen

waxing, waning, waxing and waning, more...

gradual, moon, sphered, total, own, last, rapid, corresponding, inch, unsnuffed, middle

lose vigor,   to fade,   lose intensity,   to fade away,   grow weak,   gradually diminish,   to pale,   slowly fade,   gradually fade,   lessen over time