I am sure that the word late as in tardy does not have the same origin. It certainly does not correlate with the terms.
I wonder if the actual suffix is closer to "olate" given my aforementioned terms.
Learn English – the origin and meaning of the suffix -late, as in “isolate” and “desolate”
etymologysuffixes
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Best Answer
The suffix involved is '-ate', and it reached the English nouns (or adjectives) by two different routes. OED gives '-ate' in 'isolate' as
'Isolate' reached English from Italian isolato (and French isolé), themselves deriving from Latin insulātus.
For 'desolate' (noun and adjective), the route was more directly from Latin dēsōlātus, past participle of dēsōlāre.
The verbs 'isolate' and 'desolate' also differ significantly, etymologically speaking. 'Desolate' was formed on the model of the adjective, and first occurs much later than the adjective. 'Isolate' is a back-formation from the adjective or derives from French isoler (itself from Italian isolare, which is from Latin insulāre), plus the verb suffix '-ate'.
That's all very tortuous and, as you probably gathered from mention of 'pirate' and 'frigate', the bare meaning of the suffix is not especially germane to the conglomerative meaning of the terms. More germane is the meaning of the Latin stem that gave rise to 'isolate' and 'desolate', that is, sol, meaning "alone, only".