adverb
(not) well; (not) properly; (not) enough
Used with a negative verb to mean that something is not done well, properly, or sufficiently. Often interchangeable with ろくに, but ろくろく can sound slightly more emphatic or colloquial.
See also: ろくに
彼はろくろく勉強もしないで試験に合格した。
He passed the exam without even studying properly.
ろくろく眠れなかった。
I couldn't sleep well.
Rarely used kanji form.
Rarely used kanji form.
ろくに is more common and neutral; ろくろく is slightly more emphatic or colloquial, but both are used with negatives to mean 'not properly'.
The origin is uncertain. The kanji forms are ateji (phonetic) or rarely used spellings, and the word is usually written in kana.