Pop it up out of the ground and check to see if the the root system is healthy and white. Or black and rotted? When a plants overall appearance is poor often its an unhealthy root system. Be sure the palm is planted in well drained soil and at the proper depth. Planted too low the plant would lose vigor. First check the roots --this will tell you the health of the most important part of the plant!
To give it a boost you could pour liquid fertilizer over the foliage where it will be readily absorbed. Follow the directions on the product label.