What is the true meaning of the word “wilco” when used on the radio? What is its origin?
"Wilco" is short for the phrase "will comply," meaning that the speaker will follow the instructions to which they are replying. Merriam-Webster places the origin at 1938, some time after the invention of radio, likely in military usage.

Although the phrase "roger wilco" is sometimes used, it is considered redundant since the "roger" (meaning "received and understood") is implied.