Synonyms of the word 
THANKLESS → UNAPPRECIATED - UNAPPRECIATIVE - UNGRATEFUL - UNGRATIFYING - UNREWARDING - UNTHANKFUL
thankless
- adj. (of a task) not appreciated or rewarded.
- adj. (of a person) ungrateful or unappreciative.
unappreciated
- adj. Not deemed to have any value.
- adj. (of an investment) Not having risen in value.
unappreciative
- adj. Not appreciative.
ungrateful
- adj. Not grateful; not expressing gratitude; a dissatisfied person.
ungratifying
- adj. Not providing gratification.
unrewarding
- adj. Not providing reward or satisfaction.
unthankful
- adj. Not thankful; ungrateful.
If you are interested in words, visit the following sites :
- wiktionary.org/thankless For complete definition of a word
- 1word.ws/thankless to play with words, suffixs, prefixs, etc.