linear in WordNet English dictionary

1. designating or involving an equation whose terms are of the first degree
   linear  additive 
   
2. of a circuit or device having an output that is proportional to the input
   "analogue device"; "linear amplifier"
   analogue  analog  linear 
   
3. (of a leaf shape) long and narrow
   linear  elongate 
   
4. of or in or along or relating to a line; involving a single dimension
   "a linear measurement"
   linear  one-dimensional 
   
5. measured lengthwise
   "cost of lumber per running foot"
   linear  running