What is 'swounds?
A sort of abbreviative censorship (minced oath) of "God's wounds", a phrase used in cursing in shakespearean times.
It is to that phrase as "darn" is to "damn", or "fudge" to "fuck".
"'Swounds, I should take it, for it cannot be but I am pidgeon-liver'd and lack gall to make oppression bitter, or ere this I should ha' fatted all the region kites with this slave's offal." -Hamlet, Act II, scene 2, lines 580-584