useless; vain; aimless; idle
「徒」 has other readings with different meanings.
ordinary; common; usual
vain; futile; transient; frivolous
imprisonment (for 1-3 years; third most severe of the five ritsuryō punishments)
foot soldier (Edo period); samurai on foot
徒に時間を過ごしてしまった。
I spent time in vain.
結果の出ない徒な努力は避けたいものだ。
One wants to avoid useless efforts.
徒に先のことを心配するのはやめよう。
Let's stop worrying needlessly.