different between unfruitful vs lacklustre

English

un- +? fruitful

unfruitful (comparative more unfruitful, superlative most unfruitful)

(chiefly figuratively) Not bearing fruit.
Despite going on for two hours, her search was unfruitful.

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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