marginally

Marginally means by only a very small amount. Enough to measure, not enough to matter.

It sits before a comparative, giving marginally better, marginally cheaper, marginally faster, and it is a favourite of understatement, since describing an improvement as marginally better usually means it makes no real difference. Scientific and business writing use it precisely for small differences. The adjective marginal covers the same ground and also means at the edge, as in a marginal seat or marginal land.