in conjunction with; combined
"our salaries put together couldn't pay for the damage"
"we couldn't pay for the damages with all our salaries put together"
Together, acting as one; collectively.
"The two companies jointly launched a new product to compete in the global market."
In plain English: Jointly means doing something together as if you are both sharing responsibility for it.
"The two companies jointly launched a new product last week."
The word jointly comes from combining the noun joint with the suffix -ly to form an adverb meaning "in a shared manner." This construction follows the standard pattern of adding -ly to existing words to indicate how an action is performed.