The Collaborative International Dictionary of English v.0.48:

Pumpkin \Pump"kin\, n. [For older pompion, pompon, OF. pompon,
   L. pepo, peponis, Gr. ?, properly, cooked by the sun, ripe,
   mellow; -- so called because not eaten till ripe. Cf. Cook,
   n.] (Bot.)
   A well-known trailing plant (Cucurbita pepo) and its fruit,
   -- used for cooking and for feeding stock; a pompion.
   [1913 Webster]

   Pumpkin seed.
   (a) The flattish oval seed of the pumpkin.
   (b) (Zool.) The common pondfish.
       [1913 Webster]

WordNet (r) 3.0 (2006):

pumpkin
    n 1: a coarse vine widely cultivated for its large pulpy round
         orange fruit with firm orange skin and numerous seeds;
         subspecies of Cucurbita pepo include the summer squashes
         and a few autumn squashes [syn: pumpkin, pumpkin vine,
         autumn pumpkin, Cucurbita pepo]
    2: usually large pulpy deep-yellow round fruit of the squash
       family maturing in late summer or early autumn

The Free On-line Dictionary of Computing (30 December 2018):

pumpkin
backup pumpkin
patch pumpkin
pumpkineer
pumpking

    A humourous term for the token - the object
   (notional or real) that gives its possessor (the "pumpking" or
   the "pumpkineer") exclusive access to something, e.g. applying
   patches to a master copy of source (for which the pumpkin
   is called a "patch pumpkin").

   Chip Salzenberg  wrote:

   David Croy once told me once that at a previous job, there was
   one tape drive and multiple systems that used it for backups.
   But instead of some high-tech exclusion software, they used a
   low-tech method to prevent multiple simultaneous backups: a
   stuffed pumpkin.  No one was allowed to make backups unless
   they had the "backup pumpkin".

   (1999-02-23)