thank ‧ less /ˈθæŋkləs/ BrE AmE adjective
[ Word Family: noun : ↑ thanks , ↑ thankfulness ; adjective : ↑ thankful , ↑ thankless ; verb : ↑ thank ; adverb : ↑ thankfully ]
[ Date: 1500-1600 ; Origin: thank (noun); ⇨ ↑ thanks 2 ]
1 . a thankless job is difficult and you do not get any praise for doing it
thankless task/job/chore etc
Cooking every day is a thankless task.
2 . literary a thankless person is not grateful