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fiendish
extremely cruel or unpleasant; devilish.
extremely awkward or complex.
venerable workhorse
I didnt find definition.
maybe the word means most famous tank/aircraft?
or something finally outlived its usefulness
https://fineartamerica.com/featured/the-venerable-workhorse-mike-flynn.html
venerable
accorded a great deal of respect, especially because of age, wisdom, or character.
workhorse
a horse used for work on a farm.
a person or machine that dependably performs hard work over a long period of time.
