WordNet (r) 3.0 (2006):

shell out
    v 1: administer or bestow, as in small portions; "administer
         critical remarks to everyone present"; "dole out some
         money"; "shell out pocket money for the children"; "deal a
         blow to someone"; "the machine dispenses soft drinks" [syn:
         distribute, administer, mete out, deal, parcel
         out, lot, dispense, shell out, deal out, dish
         out, allot, dole out]

The Free On-line Dictionary of Computing (19 January 2023):

shell out

   [Unix] To spawn an interactive subshell from within a program
   (e.g. a mailer or editor).  "Bang foo runs foo in a subshell,
   while bang alone shells out."

   [Jargon File]

   (1995-05-11)


The Jargon File (version 4.4.7, 29 Dec 2003):

shell out
 vi.

    [Unix] To spawn an interactive subshell from within a program (e.g., a
    mailer or editor). “Bang foo runs foo in a subshell, while bang alone
    shells out.”