coward; timid man
Literary and somewhat archaic term for a cowardly or faint-hearted person. In modern Japanese, 臆病者 (おくびょうもの) is far more common.
He fled the battlefield like a coward.
"懦夫" is an old expression; nowadays people usually say "臆病者".
From Chinese 懦夫 (nuòfū), combining 懦 'weak, timid' and 夫 'man'. The exact historical path into Japanese is uncertain, but it is a Sino-Japanese compound (kango).