My Mum-in-Law [currently awaiting a cataract operation] uses a magnifying glass to read magazines, books etc. She always calls the lens/glass her "bosser" not sure of spelling, but that's how it sounds, any ideas where that comes from?
Here's my suggestion, for what it's worth. "Bosser" may come from the medical condition that is commonly called "boss eyed". The Latin name is strabismus. Some people say that a boss-eyed person is squint-eyed, and to look at something closely is called "having a squint at it". So, maybe there's some connection between someone who is boss eyed, having a squint at, and using a lens (a squinter or bosser) because their eyesight is not good.
One of the old meanings of the verb 'to boss' - as in our modern-day word 'EMboss' - was to cause to swell or make something stand out. Accordingly, it makes good sense to call a magnifying-glass a 'bosser'.