The phrase "gradual strengthening" means the process of getting stronger or more powerful little by little over time, instead of improving suddenly or quickly. Full definition
«With ongoing job creation, wage increases and rising household formations, we can expect continued, gradual strengthening of the housing market in the coming months.» (nahb.org)
Fiscal headwinds are expected to keep growth to below 2.0 percent for the first half of the year, with gradual strengthening in the second half of 2013 and into 2014. (rismedia.com)
At the global level, 2015 was a little disappointing as the world dealt with diverging economic prospects and shifting terms of trade, but we expect gradual strengthening to resume in 2016. (bankofcanada.ca)