nag

Short definition from Wiktionary

Noun

1. 1
   A small horse; a pony.
2. 2
   An old, useless horse.
3. 3
   A paramour.
4. 4
   Someone or something that nags.
5. 5
   A repeated complaint or reminder.
6. 6
   A persistent, bothersome thought or worry.
7. 7
   Misspelling of knack.

Verb

1. 1
   To repeatedly remind or complain to (someone) in an annoying way, often about insignificant or unnecessary matters.
2. 2
   To bother with persistent thoughts or memories.
3. 3
   To bother or disturb persistently in any way.