Single word names are generally not considered to be sufficiently unique when compared to other names containing the same word and will generally not be approved. For example, “Cleaning Ltd.” would probably not be approved.
However, exceptions may be allowed in cases where the proposed single-word name is a coined word that has been trademarked, if evidence of trademark ownership is presented with the name request. For example, if you owned and could prove ownership of the trademark to the word “Fantaxial”, you might be able to name your corporation “Fantaxial Ltd.”
Obvious contractions of common words are not considered to be coined words. For example, “Naturagas”, which is an obvious contraction of “natural gas”, would probably not be considered a coined word.