The word "frivolous" originates from the Latin word "frivolus," meaning "silly, empty, trifling, or worthless."  This Latin word is thought to have been derived from the root "frivos," meaning "broken, crumbled," which itself comes from "friare," meaning "to break, rub away, or crumble," according to the Online Etymology Dictionary. 

Frivolous in British English is (disapproving of people or their behavior) silly or funny, especially when such behavior is not suitable.  

The earliest known use of the adjective frivolous is in the mid 1500s. OED's earliest evidence for frivolous is from 1549, in the writing of John Leland, poet and antiquary.

Examples of "frivolous" used in a sentence:  
"There are those who scoff at the school boy, calling him frivolous and shallow." 
"But this was Nero, and he would not be Nero without being frivolous." 
"Some of the prayers were rather frivolous." 
"We momentarily move onto more frivolous things."
"That all things silly or frivolous have no right to exist."
"He exudes an easy blend of the serious and the frivolous."

Just the facts:

FRIVOLOUS Definition & Meaning - Merriam-Webster