Meanings of taut bowstring in English

A cloud of horse swept down on them, each man riding loose with his hand on a taut bowstring.

"Now?" asked Bakall, holding his taut bowstring against his cheek and waiting for Iydahoe's command.

Standing a little farther away were the two elves, as tense as two taut bowstrings or the strings of some musical instrument.

Jack's nostrils quivered with the indrawing of a great gust of air and his diaphragm swelled until his ribs were like taut bowstrings.

Her shrivelled forearm, exposed by the loose sleeve, possessed no more of muscle than several taut bowstrings stretched across meagre bone under yellow, parchment-like skin.