So, I was trying to think of a word that had the opposite meaning of "latent".
Latent means "existing, yet unmanifested". I'm looking for a word that meant "existing and manifested, yet dissipating throughout his life".
For example, angry behaviour could exist in someone from an early age but then disappear over a few years... what would the adjective for that behaviour be?
It sounds as if you are seeking a word you used in your question - dissipating
to disappear gradually, or to cause something to disappear gradually: It took months of effort to dissipate the oil spill in the North Sea.
There are numerous other terms for this gradual decline, such as
- fading
- extinguishing
- exhausting
- declining
- diminishing
- depleting
- dispersing
- diffusing
- vanishing
- dissolving
- disappearing
- devolving
If you look at it as meaning "an existing thing that is unmanifested", then you could consider "extant" (an existing thing that is currently manifested) its antonym.
While perhaps not exactly what you aksed for, that word might in fact work in your case. It doesn't directly imply the thing has tailed off over time. However, that is the nature of things, so a hint of that implication is in there. There's nothing stopping you from helping it along a bit with other words ("still" being a good choice).
If that isn't enough for you, try "residual", which is more like "the amount that is still left after a lot has been used up". I don't think it qualifies as a proper antonym for "latent", but it may be the word you need.
You say latent means "existing, yet unmanifested", so an opposite would be manifest.
Features are divided into latent features and manifest features.
Manifest -- ODO
(adj.) Clear or obvious to the eye or mind.
"her manifest charm and proven ability"
The most frequently used antonymn of "latent" is "patent". Lawyers use it commonly, and it means "obvious". Latent's most common usage is closest to "hidden"--like a latent fingerprint. It is there, but you can't see it until you do something, like dust it with powder.
Nonetheless, I don't think "patent" is appropriate for what you're trying to convey. You may wish to consider "diminishes" or "becomes less frequent or less intense over time".
Waning, from wane, To decrease gradually in size, amount, intensity, or degree; decline.
