In terms of weight:
* Lighter: This is the most direct opposite, meaning having less weight.
In terms of intensity:
* Lighter: This can also refer to something less intense, such as a lighter color or a lighter tone of voice.
* Lesser: This implies a smaller degree of something, such as a lesser burden.
* Easier: This implies something less challenging or difficult.
In terms of other meanings:
* Lighter: This can also refer to something more cheerful or less serious.
To determine the most appropriate opposite, consider the specific context in which "heavier" is used.