godan verb (-su), transitive verb
retighten; tighten again
Used when something that was tightened before has become loose and needs to be tightened again. Common with bolts, screws, belts, strings, etc.
ネジが緩んでいたので、締め直した。
The screw was loose, so I retightened it.
靴ひもを締め直して、もう一度走
I retied my shoelaces and started running again.