Is there a term for this, or is it simply something a competent poet is able to pull off? Take Thom Gunn's Tamer and Hawk. Mainly in iambic trimeter unless I'm mistaken, but far from concrete in either. I thought I was so tough, But gentled at your hands, Cannot be quick enough To fly for you and show That when I go I go At your commands. Even in flight above I am no longer free: You seeled me with your love, I am blind to other birds— The habit of your words Has hooded me. As formerly, I wheel I hover and I twist, But only want the feel, In my possessive thought, Of catcher and of caught Upon your wrist. You but half civilize, Taming me in this way. Through having only eyes For you I fear to lose, I lose to keep, and choose Tamer as prey.