/ ˈɪmbəsiːl; NAmE -sl/ noun
1.
a rude way to describe a person that you think is very stupid
SYN idiot :
They behaved like imbeciles.
2.
( old-fashioned , offensive ) a person who has a very low level of intelligence
► im·be·cile (also im·be·cil·ic ) adjective [ usually before noun ]:
imbecile remarks
► im·be·cil·ity / ˌɪmbəˈsɪləti; NAmE / noun [ U , C ]
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WORD ORIGIN
mid 16th cent. (as an adjective in the sense physically weak ): via French from Latin imbecillus , literally without a supporting staff, from in- (expressing negation) + baculum stick, staff. The current sense dates from the early 19th cent.