Sentence:  Not only should every educator above the rank of instructor be expected to be a member of one of the professional organizations , but his first qualification for membership as an educator should be so sharply scrutinized that membership would <WSD>be</WSD> equivalent to certification to teach the subject . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)