1. (of a knife, pencil, etc.) having a worn-down edge or point; not sharp:

〈刃物･針などの先端が〉とがっていない(↔ sharp); 切れない, なまくらな

e.g. a blunt knife.

having a flat or rounded end:

e.g. the blunt tip of the leaf.

2. (of a person or remark) uncompromisingly forthright:

〈人･言葉･態度などが〉(不作法で･配慮がなく)思ったままの事を口にする, 露骨な; ぶっきらぼうな

e.g. a blunt statement of fact

e.g. he is as blunt as a kick in the shins.

a hollowed-out cigar filled with marijuana.

〈俗〉マリフアナたばこ

make or become less sharp:

〈刃先･先端〉を鈍らせる, 切れなくする.

e.g. with object : wood can blunt your ax

e.g. no object : the edge may blunt very rapidly.

with object weaken or reduce (something):

〈感覚･気持ち･欲求〉を鈍らせる, 弱める

e.g. their determination had been blunted.

bluntness | ˈbləntnəs | noun

Middle English (in the sense ‘dull, insensitive’): perhaps of Scandinavian origin and related to Old Norse blunda ‘shut the eyes’.