Lewis & Short

1. infirmo, āvi, ātum, 1, v. a. and n. [infirmus].

  1. I. Act., to deprive of strength, to weaken, enfeeble.
    1. A. Lit.: legiones, Tac. A. 15, 10: munimenta madore, Sall. Fragm. ap. Non. 138, 6: hominem, Cels. 2, 12.
    2. B. Trop.
        1. a. To invalidate, disprove, refute: res tam leves infirmare ac diluere, Cic. Rosc. Am. 15, 42; with tollere, id. N. D. 2, 59, 147; with frangere, id. de Or. 131: fidem testis, id. Rosc. Com. 15, 45: fidem alicui, id. Att. 15, 26.
        2. b. To annul, make void: legem, Liv. 34, 3; Quint. 7, 1, 49: contractum, Dig. 49, 14, 46: graviter ferens aliquid a se factum infirmari, Vell. 2, 2, 1: acta illa atque omnes res superioris anni, Cic. Sest. 18, 40.
  2. II. Neutr. only in part. pres. as subst.: infirmantes, um, m., the weak, sick, Sulp. Sev. Vit. S. Mart. 18, 5; id. Ep. 2, 12.