different between unproductive vs lacklustre

English

un- +? productive

unproductive (comparative more unproductive, superlative most unproductive)

Not productive; useless; fruitless.
Juggling is an amusing pastime, but generally unproductive.
(linguistics, of affixes, mechanisms of word formation, etc) No longer used to produce new words (see examples).

lack +? lustre

lacklustre (comparative more lacklustre, superlative most lacklustre)

lacklustre (countable and uncountable, plural lacklustres)

(British) Alternative spelling of lackluster
- 1990, The Nigerian Economist (volume 4, page lxxii)
  Secondly, the fear of offending the military has reduced the campaigns to mere lacklustres. Promises are reeled off with so much obvious lack of passion that it is quite possible the party bosses themselves hardly believe what they say […]

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