Glamour and grammar are historically related. The path is surprising, but it makes sense once you see the older meanings of grammar.
In medieval and early modern usage, grammar did not always mean only sentence rules and school lessons. It could also suggest learning in general, especially learned knowledge that seemed mysterious to ordinary people. In Scots, this helped create glamour, a form that became associated with magic, enchantment, and occult knowledge.
Over time, the meaning shifted again:
- grammar: learned study, especially book learning
- glamour: an enchantment or magical charm
- glamour: attractive beauty, allure, stylish elegance
So the modern sense of glamour grew out of an older idea of learning that seemed almost magical. A useful contrast is this: today, grammar usually means language structure, while glamour usually means elegance or charm. Historically, though, they come from the same word family.
That is why glamour photography and English grammar look unrelated today, even though their word history connects them.