An utter coward; a mean-spirited person; a worthless wretch. Also used as a general term of abuse. Now chiefly arch. or humorous.
“poltroon, n. and adj.” OED Online. Oxford University Press, June 2017. Web. 23 July 2017.
This is going to sound like a weird rant, but it is genuinely hard to write a female character for adventure story without making her a damsel in distress or some sex icon.