1. Not feeling or showing gratitude
   "How sharper than a serpent's tooth it is / To have a thankless child!"
   - ungrateful, unthankful 
2. Not likely to be rewarded
   "grading papers is a thankless task"
   - unappreciated, ungratifying

See also: unappreciative, unrewarding

• brunt
• Brusa
• bruschetta
• brush
• brush aside
• brush cut
• brush discharge
• brush down
• brush fire
• brush kangaroo
• brush on
• brush turkey
• brush wolf
• brush-footed butterfly
• brush-off
• brush-tail porcupine
• brush-tailed phalanger
• brush-tailed porcupine
• brushed
• brushing
• brushlike
• brushstroke
• brushup
• brushwood
• brushwork