Today's word is VALEO, which is perhaps best known from the Latin salutation, Ave atque vale, "Hail and farewell." The verb valere means to "fare well, be strong," etc. You can see the same root at work in the adjective validus, which also gives us the English "valid." Quite a few English words come from this root, as a matter of fact: prevail and countervail, for example, as well as valor and valiant. There is also the personal name Valerie; compare the Roman name Valerius.
You can use this verb in a variety of different constructions. With the preposition ad, it can mean "strong enough to do something," as in this statement by Cicero: alios videmus velocitate ad cursum, alios viribus ad luctandum valere.
It can also take the infinitive, as in this statement from Phaedrus's fable about the weasel and the mice: mustela cum mures veloces non valeret assequi.
Although the word can refer to all kinds of strength, it frequently refers to general physical well-being. For example, it is common to write at the beginning of a letter, si vales, bene est - which can be abbreviated to SVBE.
There is a wide range of metaphorical uses for this term, including the idea of monetary value. If you ask Quanti valet? you are asking how much something is worth, what is its value.
Here are some Latin sayings and proverbs using the verb valere:
Volo, sed non valeo.
Valere malo quam dives esse.
Infimus et servus quisque valere cupit.
Corpus valet, sed aegrotat crumena.
Res tantum valet quantum vendi potest.
Fodere non valeo, mendicare erubesco.
Non vivere, sed valere vita est.
Sine ope divina nihil valemus.
Deo non dante, nil valet labor.
Virtus unita valet.
Quae non valeant singula, iuncta iuvant.
Plus sonat quam valet.
Plus legibus arma valent.
Ut volunt reges, ita valent leges.
Ibi valet populus, ubi valent leges.
Plus valet humanis viribus ira dei.
Contra vim non valet ius.
Ratio contra vim parum valet.
Ratio fatum vincere nulla valet.
Fortuna plus quam consilium valet.
Testimonium unius non valet.
Plus valent oculi quam oculus.
Res plus valent quam verba.
Plus actum valet quam scriptum.
Plurimum valet gallus in aedibus suis.
Quot linguas calles, tot homines vales.
Recte valere et sapere, duo vitae bona.