Early meanings
Originally, “awful” meant “filled with awe” or “inspiring awe”. It could also mean “worthy of respect or fear”. In the 1600s, it could mean “sublimely majestic”. In the Renaissance, it could refer to something that is solemnly impressive
Later meanings
The meaning of “awful” shifted to “horrible” or “terrible”. In the early 19th century, it was used as an adverbial intensifier, such as “awful hot” or “awful cold”.