free of charge; mere, simply, just

only / simply / just

middle

work done for free, unpaid work, uncompensated work / work done in vain, work with no favorable end result

to work for free, to work without pay or other compensation / to work in vain, to work with no favorable end result

a free ride, especially on a train

(of a place) right in the middle of / (of an event) right in the midst of