1. To give up and surrender: laid down their arms.
2. To specify: laid down the rules.
3. To store for the future.
4. Nonstandard To lie down
Sorry, Powerful, we need more context. What is doing the laying/lying? If it's the airplane, we'd say 'we're coming in to land', or 'the plane will land soon'. If it's you, lucky enough to be in a first class cabin with a bed of some sort, you would say 'I'll go and lie down now'. Note: an incorrect but common usage of the verb 'to lay' (which is transitive) says: "I'll lay down for an hour or so". Hens lay eggs, mother/father lays the table (sets out the spoons, plates etc), but we/I/you lie down. The 'lay' usage may arise because of confusion with the verb 'to lie' (to tell an untruth).What's the best verb for (lay down) if you are on an airplane?