The word "conspire" comes from the Latin conspīrāre, which literally means "to breathe together".   It is made up of the prefix com- ("with, together") and spīrāre ("to breathe"), combining to suggest an agreement or a shared purpose, originally with an implied secret or malicious intent. This root is shared with other English words like aspire, inspire, and expire.  The original definition of conspire means to act or work in harmony with another to achieve a common goal.  The meaning has evolved over time to specifically mean "to plot together," often for a criminal or mischievous purpose. 

The word "conspire" came to English from the Old French word conspirer and Latin conspirare.  According to the Oxford English Dictionary (OED), the verb "conspire" was first used in English in in 1362 by the poet William Langland. 

Examples of "conspire" used in a sentence: 
To plan something harmful: "He suspected his colleagues were conspiring to sabotage his project."  
     I had a persecution complex and thought people were conspiring against me.
For events or circumstances to come together: "It felt like the universe was conspiring to prevent him from reaching his goal." 
     "Events conspire to leave her alone on the streets of London."
To secretly plot an illegal act: "The two spies conspired to steal the classified documents". 
     "The criminals conspired to rob the bank." 
When many things work together to create a specific outcome: "The combined effects of the cold and the wind conspired to make travel difficult." 
     "Bad luck and poor timing conspired against the team's efforts to win."