"I throw fish onto the floor."
Translation:Pisces in pavimentum iacio.
Solum as an adjective means alone, yes.
Solum is also a noun that means floor, ground, foundation, bottom layer, etc. and is the origin of sole as we use it to mean the bottom of a foot or shoe.
My question was why it's translating pavimentum, a specific type of flooring and road surface common to Roman infrastructure, is translated to "floor" instead of more accurately to "pavement", and why "solum", which has the same generic meaning as "floor" does in English, is not allowed.