First off, the Broadway straight refers to a hand of AKQJT and is the highest value straight in Poker. Similarly any of those cards are sometimes called Broadway cards. Now as to the origin of the term in poker, that like most of the slang is probably quite difficult to pinpoint, if even possible to locate at all. I have done a quick search and can find no theory of origin. In general locating the origin of terms in poker is very difficult -- it seems our early players were not the writing type.
However the term is more than appropriate. Broadway is by some seen as the pinnacle of theatre, and does have one of the highest densities of theatres in the world. In the same light the ace high straight in poker is the best possible straight. Thus an expression like "You can't beat broadway" makes perfect sense in both poker and theatre.
The word Broadway used to be used a lot to describe someone or something that was extremely flamboyant and over the top. You can't get much more like that than an ace-high straight.
Lawn Bowling
The medical term for straight is Heterosexual.The term for being straight, sexually, is heterosexual.
Railroad - this term is actually an American term; however, the word 'rail' originates from the Latin word, regula, which means: straight rod.
There really is only one good slang term for Broadway. It's called the Great White Way.
If by "straight back" you mean "directly behind the aircraft" then the term is "6 o'clock" or "my/ your six".
bent.
In the 60's, a slang term used by subculture, associated with "give me the straight skinny", a narrow honest truth. Damn straight means no curves or wiggle room, just straight truth. "give me a straight answer"
that entire song is pretty much about hookers/strippers, etc. So daffy-dills is probly referring to them.
Yes, that's the usual term. heterosexual = straight homosexual = gay
The Latin word for straight (in the sense of not curved) is rectus or directus.
Golf
A ruler is a straight edge