reason

That which causes something: an efficient cause, a proximate cause.

How to use

In formal and informal contexts, 'reason' is often used to describe the underlying cause or motivation behind a particular action, decision, or event. For instance, 'The reason for the delay was unforeseen circumstances.' Note that 'reason' can sometimes be confused with 'cause', but while 'cause' typically implies a more direct or immediate effect, 'reason' suggests a more underlying or motivating factor. This nuance is particularly important in academic and professional writing.