These words refer to a lack of awareness that produces slipshod, dangerous or offensive results. Heedless most strongly indicates inattentiveness, with disapproving suggestions of self-preoccupation, stubbornness or indifference to the feelings or safety or others.

• Heedless of everything but the striking impression she was making; heedless of his parents’ sound advice; He kept make caustic remarks, heedless of whom he might offend; The let out sail, headless of the gathering storm clouds.

Thoughtless is less disapproving in tone, suggesting a lapse or failure, possibly unintentional, rather than the determined disregarding indicated by heedless: a thoughtless mistake; He apologized for having been so thoughtless of her feelings. Consequently, it can be used euphemistically for heedless , although it occasionally expresses disapproval in its own right: the typically thoughtless and irresponsible behaviour of teenagers.

Inconsiderate relates most closely to heedless , and insensitive to thoughtless . Both words, however, concentrate more on doing injury to the feelings of others. Inconsiderate expresses almost as much disapproval as heedless in pointing to conscious, if not deliberate, discourtesy towards others: his inconsiderate insistence on playing the radiogram when his roommates were trying to study. Insensitive may suggest that the discourtesy is unintentional in that it stems from a lack of understanding of other people’s needs: insensitive to their strong disapproval of his dropping in on them unannounced. The word also suggests, more than any other word here, a lack of awareness of finer shadings of meanings: insensitive to the nuances of diplomatic protocol.

Careless is the most general of these words and can substitute, with a loss of preciseness, for any of them, regardless of the area of meaning involved. Most commonly, however, it is closest to incautious in indicating a heedless attitude to standards of accuracy or safety; laziness, indifference or preoccupation may be suggested as possible reasons for the housekeeping; a sense of false safety that made them careless about locking their door at night; so rushed that he grew careless in adding up the last attitude towards safety, with the suggestion that this results from a thoughtless or insensitive recklessness: incautious about letting the children play out in the street.