On the Tip of My Tongue

Having a very vocal 2-year old is quite a humbling experience: it's revealing a lot about my own vocabulary gaps.
And I don't just mean in French.
There seem to be whole areas of the English language that I have never had any need to explore before... and which therefore remain a mystery to me.

Sometimes I feel guilty that I'm halting BB's linguistic development.
The other day, for example, my curious little boy ran over to me, wide-eyed and quite scared, to ask what was making the loud "brum brum" (see, my vocab is limited) noise he could hear on the other side of the garden.
As far as I could tell, the noise was coming from a sort of "road sweeper vehicle-type thingy" on the road out the back, but we couldn't see it through the trees.
Stumped, but duty-bound to provide an answer for BB, I stuttered: "Er, well, that's called a... a machine!"

Pretty lame, I know, and unfortunately, BB grasped this word at once and has hung onto it ever since. Only, he now thinks a "machine" is specific to a scary, noisy road-sweeper vehicle thing.
So every time we hear a rumbling noise outside, he looks at me with big startled eyes and asks "C'est 'chine? 'Chine?"
"Yes, honey," I nod weakly, "It's the machine."

Does anyone happen to have a specialist "trucks, machinery & other road vehicles" dictionary they could lend me?
Er, preferably with pictures?