O constant plecity? (8)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

I’m sure this is very clever and probably staring me in the face but I can’t see beyond TAN (constant) and ‘city’; I’m pretty sure that, as soon as I’ve posted this, the first half dozen or so comments will put me right – thanks in advance Please see comments 1 and 2