'Witness' in the Bible

and a man is intimate with her, and it is hidden from the eyes of her husband and it is kept secret, although she has defiled herself, and there is no witness against her and she has not been caught in the act,

‘If anyone kills a person [intentionally], the murderer shall be put to death on the testimony of [two or more] witnesses; but no one shall be put to death on the testimony of [only] one witness.