Sentence:  [...] and in the absence of other signs, or when these latter are inconclusive, it is extremely useful. But it is not, under any circumstances, <WSD>absolute</WSD> evidence of the syphilitic nature of a given symptom or set of symptoms. 
Meaning of the word marked with <WSD> tags:  Positive, certain; unquestionable. (first attested in the early 1600s)