'Halves' is the plural of 'half'. 'Halve' is a also a verb. The present government has almost halved the number of unemployed people. He cut the cake into two equal halves.

Half a league, half a league onwards ... (The Charge of the light brigade - Tennyson) Before they had gone half way their number was halved; they never did things by halves (apart from dying).

Half is singular and halves is plural. "halve" in its form that you are asking of, is actually a verb.

Half is the singular, and halves is the plural.