From earlier rōbus (with change of nominative after the pattern of iecur), from Proto-Italic *rouβos, from Proto-Indo-European *h₁rewdʰ- (“red”), named for its reddish hardwood and thus cognate to ruber.
noun
declension-3an oak tree
declension-3Designating a specific kind and opposed to quercus, aesculus.
declension-3hardness
declension-3strength
“In ūniversum aestimantī plūs penes peditem rōboris.” — In general, to one estimating, more of their strength is in their infantry.
“Satis natura dedit roboris si illo utamur.” — Nature has given us enough strength, if only we would employ it.
“...atque Hispaniensis, quae multo plus firmamenti ac roboris habebat” — And the Spanish, who had very great support and strength...