WordNet (r) 3.0 (2006):

spiffy
    adj 1: marked by up-to-dateness in dress and manners; "a dapper
           young man"; "a jaunty red hat" [syn: dapper, dashing,
           jaunty, natty, raffish, rakish, spiffy,
           snappy, spruce]

Moby Thesaurus II by Grady Ward, 1.0:

83 Moby Thesaurus words for "spiffy":
   OK, ace-high, bad, bandbox, bang-up, bonzer, boss, braw, bully,
   but good, chic, classy, clothes-conscious, cool, corking,
   cosmopolitan, crackerjack, dandy, dapper, dashing, delicious,
   doggy, dressed to advantage, dressed to kill, ducky, elegant,
   exquisite, fab, fine and dandy, gear, genteel, great, groovy,
   heavy, hot, hunky-dory, jam-up, jaunty, just dandy, keen, marvy,
   mean, natty, neat, nifty, nobby, okay, out of sight, peachy,
   peachy-keen, posh, recherche, ripping, ritzy, rum, sassy,
   scrumptious, sharp, slap-up, sleek, smart, smashing, smug, snazzy,
   soigne, soignee, solid, something else, sophisticated, spiffing,
   spruce, stunning, style-conscious, swank, swanky, swell, tough,
   tricksy, trig, trim, well-dressed, well-groomed, wizard



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

spiffy
 /spi'fee/, adj.

    1. Said of programs having a pretty, clever, or exceptionally well-designed
    interface. ?Have you seen the spiffy X version of empire yet??

    2. Said sarcastically of a program that is perceived to have little more
    than a flashy interface going for it. Which meaning should be drawn depends
    delicately on tone of voice and context. This word was common mainstream
    slang during the 1940s, in a sense close to 1.


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

spiffy

   /spi'fee/ 1. Said of programs having a pretty, clever, or
   exceptionally well-designed interface. "Have you seen the
   spiffy X version of empire yet?"  This was common
   mainstream slang during the 1940s.

   2. Said sarcastically of a program that is perceived to have
   little more than a flashy interface going for it.  Which
   meaning should be drawn depends delicately on tone of voice
   and context.

   [Jargon File]