Misbe'ave lacking character after function (4)

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

SIN (as a verb = misbehave), with H (the character lacking in Cockney pronunciations of words such as “misbe’ave”) after it. Mathematical notation for the “hyperbolic sine” function. It’s a long time since I studied pure maths and I won’t attempt to explain what this means; I suspect most readers of this blog won’t want a long discussion on the subject. This Wikipedia article may or may not help.