What a lovely word this is to say, the attack of the “g”, the self-satisfied “ump” and the bold closing rush of the “shun”. It’s a bold, tough, dour word, and that’s pretty much what it means.
Common sense, mother wit, shrewdness, says the Shorter Oxford, though in America and probably in Australia it seems to have more the connotation of resourcefulness, drive, the courage to take something (or someone) on.
But did you know was a term used in painting? According to Sir Walter Scott gumption is the art of preparing colours; and in this 1854 dictionary it’s a medium used for preparing colours: