Yeoman's Service Meaning

Example : 1891, Charlotte Mary Yonge, Unknown to History, ch. 7:  He hath done yeoman's service, and proved himself staunch and faithful.c. 1600, William Shakespeare, Hamlet, act 5, sc. 2:  I once did hold it, as our statists do,  A baseness to write fair and labour'd much  How to forget that learning, but, sir, now  It did me yeoman's service.1827, Sir Walter Scott, The Chronicles of the Canongate, ch. 1:  [O]n many occasions his liberality did him genuine yeoman's service.