It depends on which type of trade you're in, actually lot of skills required to get success in trading. Partially we can accept that the trading as gambling because along with skills and knowledge luck matters in trading. Once if anybody tastes success while trading by sheer luck they can term it as gambling.
Well i think trading is not be considered as a gambling because when you say trading meaning you have to sell in order to get more money or extra income. Things that you considered as gambling is when you win or lose in some fight involving large amount of money, furthermore gambling is dealing with winning while tradings is dealing with the value or prices of what you have sell..so trading is not considered as gambling.