Definition of "gain weight"

gain weight

verb
third-person singular simple present gains weight, present participle gaining weight, simple past and past participle gained weight
1. (intransitive) To become more heavy or obese.
2. To be taken more seriously. (of an idea, view etc.)
  Quotations
  This view gaining weight, steps were taken to reopen negotiations with the L.N.W.R.
  1939 July, John D. Hewitt, “Some Notable British Main Lines: 1. Settle and Carlisle, L.M.S.R.”, in Railway Magazine, page 35