Dictionary.net

The fruit or produce first matured and collected in any season, of which the Jews made an oblation to God, as an acknowledgment of his sovereign dominion; the first profits of anything; as, (a) in old feudal tenures, one year's profit of the land after the death of a tenant, which was paid to the king; (b) in the Church of England, the income of every spiritual benefice for the first year, paid originally to the crown, but now to a board, which applies the money so obtained to the supplementing of the incomes of small benefices; the first or earliest effect of anything, in a good or bad sense; as, the first-fruits of grace in the heart, or the first-fruits of vice.