What is the meaning of ?

The hiragana syllable (mu). Its equivalent in katakana is (mu). It is the thirty-third syllable in the gojūon order; its position is (ma-gyō u-dan, row ma, section u).

A mumbling sound.

used to form the suppositional / volitional / hortative form of verbs, equivalent to modern (-u >) / よう (-yō); also used as a mild imperative

Source: wiktionary.org