Insure, v. t. [imp. & p. p. Insured; p. pr. & vb. n. Insuring.]
Etymology: [OE. ensuren, prob. for assuren, by a change of prefix. See 1st In-, and Sure, and cf. Assure, Ensure.]
[Written also ensure.]
1. To make sure or secure; as, to insure safety to any one.
2. Specifically, to secure against a loss by a contingent event, on certain stipulated conditions, or at a given rate or premium; to give or to take an insurance on or for; as, a merchant insures his ship or its cargo, or both, against the dangers of the sea; goods and buildings are insured against fire or water; persons are insured against sickness, accident, or death; and sometimes hazardous debts are insured.
1 other Webster entry under this spelling
Insure, v. i.
To underwrite; to make insurance; as, a company insures at three per cent.
Shades of meaning
Fernald lists insure only as an antonym, under augur.
He lists it without comment; the entries above explain its neighbors.