1550s, "directly forward, right ahead," from straight (adj.1) + forward (adv.). In reference to language, from 1806. Related: Straightforwardly; straightforwardness.
he is not being as straightforward as it appears
a straightforward set of instructions
straightforward in all his business affairs
a straightforward gaze
straggler
straight
straight-edge
straighten
straight-faced
straightforward
strain
strainer
strait
straiten
straitened