to make a secret agreement or form secret plans, often in collaboration with other people, in order to commit some wrong, harmful, or unlawful act, i.e. to form a conspiracy;
e.g. His colleagues began to conspire against him out of jealousy.
(verb)
to work together or seem to be acting in harmony in order to reach some common end, often one that is negative or undesirable;
e.g. She is worried that circumstances will conspire to delay her journey.