Today's word is LOCUS, which is a second-declension noun, masculine in gender. Even though the noun is masculine, note that you will also find the plural loca (meaning connected places, i.e. a "region"), in addition to the usual plural loci.
Latin meaning and usage: The basic meaning of locus is a "place" or a "spot," and it covers very much the same range as the English words do. One important additional meaning of the Latin word is what we would call "topic" or "subject" in English (and the English word "topic" is itself derived from the Greek word for place).
Latin word formation: The word locus is a basic root word in Latin and gives rise to many compounds and derivatives. There is a diminutive form of the noun, loculus, meaning a little chest or casket. There are verbs formed from this root, such as locare, "to place, arrange," and collocare, "to set up, employ, station." Someone who is locuples is wealthy. One thing to be careful of is not to confuse the root loc- (place) with the root loq- (speaking) which also shows up as loc- in some forms (e.g., loquor-locutus).
English cognates and derivatives: We actually use the word "locus" in English to mean "a place," especially a center of activity or concentration. There are also many English words derived from this root, such as "local" and "location" - and even the "locative" case. There are also compounds like "locomotion" and "locomotive." Finally, when you use the French phrase "in lieu of" in English, you are also using a French word - lieu - that is derived from the Latin.
Here are some examples of today's word in Latin sayings and proverbs; for more information, see the page at the Scala Sapientiae, which also contains notes on some of the proverbs cited below, as well as additional proverbs:
in loco parentis
Da locum melioribus.
Nemo timendo ad summum pervenit locum.
Locus medius tutus est.
Medius locus semper tutus.
Virtus omni loco nascitur.
Metus cum venit, rarum habet somnus locum.
Ad locum unde exeunt, flumina revertuntur ut iterum fluant.
Locis remotis qui latet, lex est sibi.
Incertum est quo loco te mors exspectet; itaque tu illam omni loco exspecta.
Nonne ad unum locum properant omnia?
In mutando locum non mutant poma saporem.
Est locus unicuique suus.
Non fit hirsutus lapis per loca multa volutus.
Puer, sacer est locus; extra mingito.
Ite procul; sacer est locus; ite profani.