E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Persevere (3 syl.).
This word comes from an obsolete Latin verb, sevro (to stick rigidly); hence sevrus (severe or rigid). Asseverate is to stick rigidly to what you say; persevere is to stick rigidly to what you undertake till you have accomplished it. (Per-sevro.)