It occurs as a mineral niter and is a natural solid source of nitrogen.

My colleagues, every statement I make today is backed up by sources, solid sources.

It is used to describe rumors with actual, solid sources or reasons.

Any of those small failings can be made up for; we redirect our energies and find more solid sources of self-esteem.

This was the end of a solid source of income.

In a recent conversation, this seemed a more solid source of pride.

Thanks @somemightsay for raising the issue and thanks @spike25 for coming up with such a solid source of information.

"Gifts for Good Children" is a solid source of information on the almost endless categories that make up children's china.

Without a solid source of light, their movements were more ungainly, less controlled.

Beside, it includes a library and conference hall and the car park creates a solid source of income to get by.