Fertilizer for the Dentist?

After some x-rays and preliminary work for a crown, I went to make my next appointment and pay (some) of my bill. I was talking with a dental assistant that knows no English and had previously complimented me on my Spanish when she was getting all the info from me when I first got there.

We were doing fine and then she said something about an abonao. I say something about because we were chatting just fine and that word caught me and I forgot the sentence. Not wanting he to think I was less than brilliant in Spanish, I went on to the payment part of our meeting. All when well and I went home thinking about that word.

There are lots of words I don know in Spanish. The thing was, this was a word I did know but couldn't remember where it had been used. It turns out that besides meaning payment (her use) it also means fertilizer. Thus, I had learned it from my gardener. It's a stretch but I guess I can see how the two words are related.