by-stroke

noun2

1. •
   An incidental or slyly given stroke; a gratuitous addition or indirect action.

   • These persons are selected, for a by-stroke of satire, as drunken and riotous paupers . — 1875
2. •
   A secondary attack.

   • On his way he could not resist the temptation of dealing a by-stroke at the Petchenegans. — 1880