"linear" refers to something that follows a straight or direct path, without any curves or deviations. It can also describe a relationship or progression that is constant and goes in one direction without changing. Full definition
Further quantitative analyses of species environment relationships suggested the use of linear regression models. (judithcurry.com)
The second part of the gameplay is a much more linear model, with you walking along a nightmare path devised by the villain, which involve puzzles and nerves of steel. (thexboxhub.com)
Always keep in mind that strength and size are not linear in relationship. (liftingrevolution.com)