"lax" is an actual word. http://www.thefreedictionary.com/lax
I never got anything out of someone telling me to "relax." I often find people who use the word relaxed are not relaxed themselves, and also don't know how to convey what they mean. Or might not even know themselves what they mean.
When I work with someone, if they're muscling or straining, I'll stop for a second and ask them to do something along the lines of, "Hey, walk towards me like you're going to hand me a Coke." From there, every time, I see this person switch back into their own casual energy. Then I'll usually ask them to notice how their body feels...how their muscles are loose...how they have a light grip on the glass. I'll even squeeze their triceps and biceps, and say, "See how soft all this is. And see how you're shoulders are down."
So, with that same energy that you'd walk over and hand a Coke to someone - let's work with that same energy. And when you start to move, make it feel more like you don't give a shit. Just be in your own energy. The same energy as when you're doing something you enjoy doing, like when you hang out at home, or go to the movies, or walk through the park.
Lax = not giving a shit. Re-lax = go back to not giving a shit.
It's just extending some permission slips to people; letting them know they already know how to do this. It's simple. No need to make it into more work than it needs to be. That in being themselves, in their own energy, is the strongest and most effortless place to be. And that's exactly where the power of aikido lies.