speedworthiness en · NOUN
Etymology
From speed + worthiness, or speedworthy + -ness.
Meanings
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(rare, uncountable) The ability to travel at high speed.
The "Merchant Navy" class locomotives have lost none of their speedworthiness in the extensive rebuilding and this was certainly a good example of their prowess.
1959 October 14, O. S. Nock, “British Locomotive Practice and Performance”, in Railway Magazine, page 705: