to soil is a form of:

Credential



ENGLISH MEANING
noun
1.
That which gives a title to credit or confidence.
2.
Testimonials showing that a person is entitled to credit, or has right to exercise official power, as the letters given by a government to an ambassador or envoy, or a certificate that one is a duly elected delegate.
adjective
1.
Giving a title or claim to credit or confidence; accrediting.