Lewis & Short

grandĭo, īre, v. a. and n. [grandis] (ante-class.).

  1. I. Act., to make great, increase, enlarge: grandire est grandem facere, Varr. Rer. Divin. Lib. I.: cum aut humus semina concipere non possit, aut recepta non reddat, aut edita grandire nequeat, Plaut. Aul. (1, 1, 10): Testudineum istum tibi ego grandibo gradum, Non. 115, 1 sq.
    Mid.: nec grandiri frugum fetum posse, nec mitescere, to become great, to grow (cf. grandesco), Pac. ap. Non. 115, 11 (Fragm. Trag. v. 142 Rib.).
  2. II. Neutr., to become great, to grow: Mars pater, te precor, uti tu fruges, frumenta, vineta virgultaque grandire beneque evenire sinas, Cato, R. R. 141, 2.