Green’s Dictionary of Slang

hen v.

to act cautiously; to back down [the timidity of the fowl].

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[UK]‘Bill Truck’ Man o’ War’s Man (1843) 263: I’ll be hung, now, if Barny’s not beginning to hen.

In phrases

hen it up (v.)

to render effeminate [hen n. (1)].

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[UK]W. Talsman Gaudy Image (1966) 17: ‘What’s yours?’ Passion Rat asked? ‘My handle? [...] I’ve been known to hen it up a bit.’.