Definition of "chancy"

In winter steam contributes a fairly high proportion of its tractive effort, say 15 per cent, to heating the train. Diesels have at the moment separate oil-fired boilers which are somewhat chancy affairs, and only electric locomotives grab unlimited power for heating which does not affect their punctuality.

1960 April, G. F. Fiennes, “Unpunctuality - the cause and the cure”, in Trains Illustrated, page 244

You might think it's foolish / This chancy rendezvous / (You might think) You might think I'm crazy / (All I want) All I want is you

1984, Ric Ocasek, “You Might Think”, in Heartbeat City‎, performed by The Cars