Definition of fort noun from the Oxford Advanced Learner's Dictionary

fort

noun
fɔːt
 
; fɔːrt
 
 
1 a building or buildings built in order to defend an area against attackthe remains of a Roman fort2 (North American English) a place where soldiers live and have their trainingFort Drum
Idioms

hold the fort

(British English) (North American English hold down the fort) (informal) to have the responsibility for something or care of somebody while other people are away or outWhy not have a day off? I'll hold the fort for you.