A companion to Familia Romana, p174, adverbial, plus. What is meant by ‘adv+n.noun’?

Latin Learning Latin
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Salvete

My usual practice as I work my way through LLPSI is to use the companion volume ‘A Companion to Familia Romana. I’m just reviewing chapter XIX and have found a tiny detail on page 174 of the companion that has me puzzled. The page reviews the vocabulary introduced in that chapter.
In the section of adverbs the word ‘plus’ is given followed by (adv. + n.noun). Similar entries with prepositions appear, which I understand, but I cannot fathom the meaning here. Perhaps I’ve simply missed something obvious but I’m very keen to know what this means. Could anyone kindly help with this. I’ve tried googling but not found anything helpful yet.

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I now think I’ve simply been over thinking this and that the, perhaps, obvious answer to my question is the correct one and that the author, in my humble opinion, wished to convey that the word is also a neuter noun. I think elsewhere in the series (LLPSI) this is more explicit. Perhaps it is unfortunate that the ‘+’ symbol was used rather than a ‘,’. Having said that I wonder if again I simply have missed the point…