What another word for constructive interference?

There isn't a single perfect synonym for "constructive interference" that captures all its nuances. However, depending on the context, some good alternatives include:

More technical:

* Reinforcement

* Superposition (specifically when referring to wave amplitudes adding)

* In-phase interference

More general:

* Amplification

* Enhancement

* Strengthening

The best choice will depend on the specific context and what you want to emphasize.