"Sustain" is a complete word on its own, and it's not typically used as a base word to create other words with suffixes.
However, there are words related to "sustain" that use suffixes, like:
* Sustainable (using methods that do not deplete natural resources)
* Sustainably (in a sustainable way)
* Sustainability (the quality of being sustainable)
* Sustainer (someone or something that sustains)
If you're looking to create a new word related to "sustain", you could potentially use suffixes like "-able", "-ance", "-ment", "-ing", or "-tion", but these would need to be carefully considered in context.