Today's word is the adjective SOLUS, which is one of those adjectives that is partially a first- and second-declension adjective, but with a genitive in -ius for all genders, solius, and a dative in -i, soli. It is very important to be aware of the declension of all of these adjectives - solus, unus, totus, alius, alter, ullus, nullus, uter, and neuter - since they are all very commonly used in Latin.
Latin meaning and usage: The basic meaning of solus is "only, alone, sole." There is also an expression very similar to the English "not only... but also" - non solum... sed etiam.
Latin word formation: You can find the word in the compound adverb solummodo. You can also see the word in other compounds: soliloquium, solitarius, solitudo, etc. and also the verbal compound, desolo.
English cognates and derivatives: You can see the Latin word in the English "sole" as well as "solitary," "solitude," "soliloquy," etc. Note also the compound "desolated." We also use the Italian word "solo." One of my favorites is "solipsism," from solus+ipse, meaning the belief that one's self (ipse) is the only thing (solus) that is real.
Here are some examples of today's word in Latin sayings and proverbs; for more examples, see the page at the Scala Sapientiae, which also contains notes on some of the proverbs cited below:
Ego meorum solus sum meus.
Non sibi solum.
Non est bonum esse hominem solum.
Solus in pluribus.
Hoc solum scio, quod nihil scio.
Solum certum nihil esse certi.
Res autem durissima vivere solum.
Nemo sibi soli, sed aliis nascitur.
Soli deo gloria.
Solus non est quem diligant dii.
Cum tuus es, noli servire, nisi tibi soli.
Non nobis solum nati sumus.
Homo non sibi soli natus, sed patriae.
Sapiens nusquam minus solus quam cum solus.
Solum bellum gignit pacem.
Sola pecunia regnat.
Si pro te solo oras, pro te solus oras.
Sola virtus gaudium perpetuum.
Non in solo pane vivit homo.
Lupus, quando te solum invenit, audacior est.