名詞 imbecile:

1. a person of subnormal intelligence
   同義詞：idiot, cretin, moron, changeling, half-wit, retard

形容詞 imbecile:

1. having a mental age of three to seven years
   同義詞：imbecilic, idiotic

im.be.cile

n.（名詞）
A stupid or silly person; a dolt.
蠢人；傻瓜
A person whose mental acumen is well below par.
低能者：智力遠(yuǎn)在常態(tài)之下的人
A person of moderate to severe mental retardation having a mental age of from three to seven years and generally being capable of some degree of communication and performance of simple tasks under supervision. The term belongs to a classification system no longer in use and is now considered offensive.
弱智者：有中度到嚴(yán)重精神障礙的人，有三到七歲的智力年齡，在指導(dǎo)下通常能做某種程度的交流并能完成簡單的任務(wù)。這個(gè)術(shù)語屬于一個(gè)已停用的區(qū)分系統(tǒng)，現(xiàn)在被認(rèn)為是攻擊性的
adj.also （形容詞） 也作
imbecilic
Stupid; silly.
愚蠢的；傻的
Well below par in mental acumen.
弱智的：智力遠(yuǎn)在常態(tài)之下的

來源：
From obsolete French imbécille [weak, feeble]
源自 已廢法語 imbécille [軟弱的，微弱的]
from Old French
源自 古法語
from Latin imbôcillus
源自 拉丁語 imbôcillus
in- [not] * see in-
in- [不] *參見 in-
possibly bacillum [staff] [diminutive of] baculum [rod] * see bak-
可能為 bacillum [棍棒] [] baculum的小后綴 [棒條] *參見 bak-

【引伸】
im.becilely
adv.（副詞）