碌 is a bound form (b.f.) that rarely stands alone. It has two pronunciations with distinct meanings: lù (common) in words like 忙碌 (mánglù, busy) and 庸碌 (yōnglù, mediocre/undistinguished); and liù (this row's pinyin) in the rare word 碌碡 (liùzhou, a stone roller). The provided English gloss ('busy; undistinguished') actually describes the lù reading, not the liù one. In any case, 碌 only appears as part of multi-character compounds.