It's hard to determine what I'm looking at b/c of whatever you have wrapped around it. My best guess is whatever sits on op of the outlet assembly which is #9 in the diagram here:

Water Pump (Type-S) for 2005 Acura RSX | OEMAcuraPart

www.oemacuraparts.com

 

That appears to be the air-assist valve. Here's a related thread:

"That part which always breaks": Idle...

It seems like all of us have snapped this off at one point or another and usually, it causes panic because it is often the first piece we actually broke, ourselves, while working on our RSX's. It is Idle Air-assist Valve and is the the tee-shaped plastic tree which sits atop the coolant neck on...

www.clubrsx.com

 

Yep, idle air assist. You can get a delete kit for $30 or so or just cut that flush and tape over it if you want a cheap fix. It’s designed to warm the car up faster on cold starts by raising your idle but will still work just fine with that taped up.

 

There are a number of these available used on ebay, but from what I've read you can also use the part from a 2007 Civic Si (36281-RTA-003) which I found for about $22 on Amazon: https://www.amazon.com/36281-RTA-00.../dp/B08JLSS537/ref=sr_1_3?dchild=1&keywords=36281-RTA-003&qid=1634049002&sr=8-3

 

I broke mine as well lol, and I found another one on eBay for $50 or try a junkyard. It's called "Air Assist Valve Solenoid Coolant Sensor"
Its from an Accord but its still a Honda so you'll be fine. Do not go to Acura either, they will charge you $200 for a whole kit.

03-05 Honda Accord K24A4 air assist valve solenoid coolant coolant sensor OEM 2 | eBay