Thoughtless means not considering how other people are affected. Playing music at midnight, or taking the last of something.
The fault is inattention rather than malice, which is what makes the word useful, since calling somebody thoughtless accuses them of not noticing rather than of cruelty. A thoughtless remark is one that landed badly without being meant to. Its opposite, thoughtful, has two senses, meaning both considerate and deep in thought, and only the first is the true mirror of this word. The adverb is thoughtlessly.
1adjectivethoughtlessNot thinking about how your actions affect others.
“It was thoughtless of him not to ring.”
Proto-Indo-European
*teng-
Middle English
thought
English
thought
English, today
thoughtless
Built from
From thought + -less. thought comes from Middle English thought. From Middle English thought, ithoȝt, from Old English þōht, ġeþōht, from Proto-West Germanic þą̄ht, from Proto-Germanic þanhtaz, gaþanhtą (“thought”), from Proto-Indo-European teng- (“to think”). Cognate with Scots thocht (“thought”), stq Toacht (“thought”), West Frisian oandacht (“attention, regard, thought”), Dutch gedachte (“thought”), German Andacht (“reverence, devotion, prayer”), Icelandic þóttur (“thought”). Related to thank, think.
Etymology from Wiktionary, CC BY-SA