keep a tight rein on

keep a tight rein on (third-person singular simple present keeps a tight rein on, present participle keeping a tight rein on, simple past and past participle kept a tight rein on)

1. To exercise strict control over; keep in check.
   • 1960 April, J. P. Wilson, E. N. C. Haywood, “The route through the Peak - Derby to Manchester: Part Two”, in Trains Illustrated, page 226, photo caption:

     Class "8F" 2-8-0 No. 48501 keeps a tight rein on heavily loaded northbound hoppers as it descends the 1 in 90 gradient.

• “keep a tight rein on”, in Lexico, Dictionary.com; Oxford University Press, 2019–2022.