1) The first martyr in any cause 
• (n.) The first martyr; the first who suffers, or is sacrificed, in any cause; -- applied esp. to Stephen, the first Christian martyr.
Pro'to·mar`tyr noun [ Late Latin , from Greek ...; ... first + ... martyr: confer French protomartyr . See Proto- , and Martyr .] The first martyr; the first who suffers, or is sacrificed, in any cause; -- applied esp. to Stephen, the first Christian martyr. 
the first Christian martyr, Saint Stephen. · the first martyr in any cause.