长

cháng - length; long; forever

This is a very basic word, but I never know when to pronounce it cháng, and when zhǎng. The latter, it seems is either a verb meaning to grow, to increase etc., or an adjective meaning head or chief. I picked the word today because I was hoping to record some flagella lengthening, but sadly failed. I'm still not sure that I picked the right pronunciation, but 加长 (jiācháng) means 'lengthen'.