The Collaborative International Dictionary of English v.0.48:

Reinforcement \Re`in*force"ment\ (-ment), n.
   See Reenforcement.
   [1913 Webster]

WordNet (r) 3.0 (2006):

reinforcement
    n 1: a military operation (often involving new supplies of men
         and materiel) to strengthen a military force or aid in the
         performance of its mission; "they called for artillery
         support" [syn: support, reinforcement, reenforcement]
    2: information that makes more forcible or convincing; "his
       gestures provided eloquent reinforcement for his complaints"
       [syn: reinforcement, reenforcement]
    3: (psychology) a stimulus that strengthens or weakens the
       behavior that produced it [syn: reinforcing stimulus,
       reinforcer, reinforcement]
    4: a device designed to provide additional strength; "the
       cardboard backing was just a strengthener"; "he used gummed
       reinforcements to hold the page in his notebook" [syn:
       strengthener, reinforcement]
    5: an act performed to strengthen approved behavior [syn:
       reward, reinforcement]