archaic/literary form of 'straight' — directly or upright; not bent or crooked (e.g., 'go straight ahead').
道を真直ぐに進めば、駅が見えます。
If you go straight down the road, you'll see the station.
彼は真直ぐな背筋で立っていた。
He stood with his back perfectly straight.
真直ぐに答えないで、はぐらかすのはやめなさい。
Stop evading the question instead of answering directly.
archaic/literary sense meaning 'straightforward, honest, frank' — a person who is direct and sincere.
彼女は真直ぐな人柄で、嘘をつくことはない。
She is straightforward and would never tell a lie.
親に対して真直ぐに気持ちを話した。
I spoke honestly to my parents about how I felt.