The Collaborative International Dictionary of English v.0.48:

Insertion \In*ser"tion\, n. [L. insertio: cf. F. insertion. See
   Insert.]
   [1913 Webster]
   1. The act of inserting; as, the insertion of scions in
      stocks; the insertion of words or passages in writings.
      [1913 Webster]

   2. The condition or mode of being inserted or attached; as,
      the insertion of stamens in a calyx.
      [1913 Webster]

   3. That which is set in or inserted, such as a word or
      passage in a composition, or a narrow strip of embroidered
      lace, muslin, or cambric; as, there were numerous
      insertions and corrections to the first draft.
      [1913 Webster +PJC]

   4. (Anat.) The point or part by which a muscle or tendon is
      attached to the part to be moved; -- in contradistinction
      to its origin.
      [1913 Webster]

   Epigynous insertion (Bot.), the insertion of stamens upon
      the ovary.

   Hypogynous insertion (Bot.), insertion beneath the ovary.
      [1913 Webster]

WordNet (r) 3.0 (2006):

insertion
    n 1: a message (spoken or written) that is introduced or
         inserted; "with the help of his friend's interpolations his
         story was eventually told"; "with many insertions in the
         margins" [syn: interpolation, insertion]
    2: the act of putting one thing into another [syn: insertion,
       introduction, intromission]

Moby Thesaurus II by Grady Ward, 1.0:

97 Moby Thesaurus words for "insertion":
   Earth insertion, LEM, LM, access, admission, apogee, aside,
   attitude-control rocket, ballistic capsule, booking, burn, capsule,
   cataloging, chronicling, deep-space ship, docking,
   docking maneuver, enlistment, enrollment, entering, entrance,
   entree, entry, episode, ferry rocket, fuel ship, impanelment,
   import, importation, importing, income, incoming, indexing,
   infiltration, infix, ingoing, ingress, ingression, injection,
   inlay, input, inscribing, inscription, insert, inset, insinuation,
   intake, intercalation, interjection, interlineation, interlocution,
   interpenetration, interpolation, introduction, introgression,
   intrusion, inventorying, leakage, listing, logging,
   lunar excursion module, lunar module, manned rocket, matriculation,
   module, moon ship, multistage rocket, obiter dictum, orbit,
   parenthesis, parking orbit, penetration, percolation, perigee,
   posting, reception, record keeping, recordation, recording,
   reentry, register, registration, registry, remark, rocket, seepage,
   shuttle rocket, side remark, soft landing, space capsule,
   space docking, space rocket, spacecraft, spaceship, tabulation,
   tessera, tossing-in