Direct and indirect

Indirect means:

1. Not directly caused by or resulting from something:
2. Not done directly; conducted through intermediaries

Direct means:

Extending or moving from one place to another by the shortest way without changing direction or stopping.

Essentially, direct means to be straight (in course or direction; i.e. direct route), straightforward, purposeful (i.e. a direct effect of Joe doing his homework was that his grades improved.)

Indirect means to be a roundabout way, accidental, side effectual (i.e. The indirect effect of the Spanish Inquisition was the economic collapse of Spain.)