Lively discussion on radio about this word today. As it's archaic, not a good cultural memory for what bowyangs were. Roughly four meanings were offered:
1. something like the Encarta definition. "pants straps: a pair of strings or straps secured around each pants leg below the knee, worn in Australia and New Zealand by agricultural workers. Their purpose is said to be to prevent insects or small animals crawling up the legs."
2. a kind of cloth garter that prevents seeds and other material from falling on the inside of your socks. I've seen modern versions of these in shops under the horribly descriptive name sock protectors.
3. something like braces. These bowyangs were worn by shearers, for the purpose of keeping their trowser legs above the mess of wool on the shed floor.
4. a strap fitted to the ejector seat mechanism of an aircraft, which deploys rapidly to push the legs of the seat occupant under him/her. This prevents the person being ejected from losing their legs as they are catapulted at great speed through the cockpit opening.
"It was March and the shearers were on strike and if everyone in Melbourne and the bush knew about it, if they imagined gangs of shearers were burning down wool sheds and setting fire to the squatters' paddocks, it was news to Jack McGrath who traveled innocently beside his team in his faded red shirt, his moleskins, bowyangs, and heavy boots."