The Collaborative International Dictionary of English v.0.48:

Strenuous \Stren"u*ous\, a. [L. strenuus; cf. Gr. ? strong,
   hard, rough, harsh.]
   Eagerly pressing or urgent; zealous; ardent; earnest; bold;
   valiant; intrepid; as, a strenuous advocate for national
   rights; a strenuous reformer; a strenuous defender of his
   country.
   [1913 Webster]

         And spirit-stirring wine, that strenuous makes.
                                                  --Chapman.
   [1913 Webster]

         Strenuous, continuous labor is pain.     --I. Taylor.
   [1913 Webster] -- Stren"u*ous*ly, adv. --
   Stren"u*ous*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

strenuously
    adv 1: in a strenuous manner; strongly or vigorously; "he
           objected strenuously to the stand his party was taking"