The Collaborative International Dictionary of English v.0.48:

Instillment \In*still"ment\, n.
   The act of instilling; also, that which is instilled.
   [Written also instilment.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

instillment
    n 1: the introduction of a liquid (by pouring or injection) drop
         by drop [syn: instillation, instillment, instilment]

Moby Thesaurus II by Grady Ward, 1.0:

28 Moby Thesaurus words for "instillment":
   absorption and regurgitation, brainwashing, catechization,
   conditioning, decoction, dictation, imbuement, implantation,
   impregnation, impression, inculcation, indoctrination,
   infiltration, infixation, infixion, infusion, inoculation,
   instillation, interpenetration, marination, penetration,
   permeation, pervasion, reindoctrination, saturation, soaking,
   steeping, suffusion