reminder

powerful, strong

lasting, permanent

constant, continual, daily

further

graphic, sharp, stark, visual, vivid

chilling, grim, painful, uncomfortable

poignant, solemn

salutary

timely

important

gentle, little, quick

final

The teacher sent a final reminder about the homework deadline before the exam.

useful

That phone call was a useful reminder to pick up milk on my way home.

act/serve as, be, provide

This old photograph serves as a powerful reminder of my grandmother's life.

give sb, issue, send (out)

The teacher sent out a reminder about the homework deadline before the weekend.

receive

need

letter, note, notice

~ about

I put a note on my fridge as a reminder about my doctor's appointment.

~ to

The email served as a helpful reminder to submit our expense reports before Friday.