I don't discuss grammar much here, because I don't feel confident in explaining all the intricacies of the various rules of Hebrew grammar. And usually it doesn't reflect much on my focus here - the meaning and origin of Hebrew words and phrases.
But there are times where issues of grammar affect our understanding of those phrases, and this is one of those occasions.
I'd like to take a look at how the letter heh is used as a definite article. This Wikipedia page gives a pretty good summary:
In traditional grammar, Hebrew common nouns have three “states”: indefinite (corresponding to English “a(n)/some __”), definite (corresponding to English “the __”), and construct (corresponding to English “a(n)/some/the __ of”). Therefore, the definite article was traditionally considered to be an actual part
of the definite noun. In modern colloquial use, the definite article is
often taken as a clitic, attaching to a noun but not actually part of
it. For example, the Hebrew term for school is בֵּית־סֵפֶר (beit séfer, “house-of book”); so in traditional grammar, “the school” is בֵּית־הַסֵּפֶר (beit-haséfer, “house-of-the-book”), but in modern colloquial speech, it is often הַבֵּית־סֵפֶר (habeit-séfer, “the-house-of-book”).
(More details and examples can be found here).
Speakers of a language generally absorb the rules of grammar, even if they can't explicitly explain them. So with an understanding of the rules above, Hebrew speakers usually can figure out what do with two words in one phrase. If there are two nouns, like bayit and sefer, without the definite article, the phrase is beit sefer, and with the definite article, the phrase is beit hasefer.
If there is a noun and an adjective, however, the heh appears twice. So "a big house" is bayit gadol, but "the big house" is habayit hagadol. Again, these are intuitive rules to anyone accustomed to speaking Hebrew.
But sometimes our familiarity with these rules doesn't work to our favor, and can lead to a phenomenon called hypercorrection, where we apply rules where they don't belong, and actually use the language incorrectly.
This is the case with three familiar Hebrew phrases: lashon hara לשון הרע, ayin hara עין הרע and yetzer hara יצר הרע.
The first source of confusion is the word ra. Meaning "evil" or "bad", it can be either a noun or an adjective. But as we saw above, the only time the heh appears only before the second word in a phrase, is when they're both nouns. So I found frequent cases, where authors said that lashon hara "literally means the tongue of evil" or ayin hara "literally means the eye of evil." This is supported further by the fact that ayin and lashon are assumed to have the feminine gender, so if ra was an adjective, it would be hara'ah הרעה.
While those phrases are still generally translated as "the evil tongue" and "the evil eye" (as well as "the evil inclination" for yetzer hara) - there is a subtle difference between ra being a noun or an adjective in these phrases, especially since they are phrases loaded with religious meaning.
In these cases, ra actually is an adjective, not a noun. As this article by the Hebrew Language Academy points out, while it's not common, there are noun-adjective phrases with heh only preceding the adjective. For example, in Bereshit 1:31, we find the phrase yom hashishi יום השישי - "the sixth day", and not hayom hashishi. In post-biblical Hebrew, we find the phrase כנסת הגדולה knesset hagedola - "the great assembly", and not haknesset hagedola.
And while ayin and lashon are generally feminine nouns, there are case where they are male, as in Eicha 4:4, Zecharia 4:14 and Tehilim 11:4. So there is no need to hypercorrect, and we can still translate the phrases as "the evil eye", "the evil tongue", and "the evil inclination."
And while we're here, let's take a quick look at the origin of each of the phrases:
Lashon hara: This term refers to malicious speech or slander. In Biblical Hebrew, the word for someone speaking this way is rechil רכיל, which provided the noun rechilut רכילות. In Rabbinic Hebrew, the phrase lashon hara was introduced (based on a related phrase in Tehilim 34:14), and distinctions were made in Jewish law between rechilut and lashon hara.
Ayin hara: This phrase appears in the mishna, for example Avot 2:11 עַיִן הָרָע, וְיֵצֶר הָרָע, וְשִׂנְאַת הַבְּרִיּוֹת, מוֹצִיאִין אֶת הָאָדָם מִן הָעוֹלָם - "the evil eye, the evil inclination, and hatred for humankind put a person out of the world." According to Safrai (on Avot), this likely refers to jealousy. It has a parallel the phrase ayin ra'ah in an earlier mishna (Avot 2:9), along with the opposite - ayin tova. In that case, the phrases are referring to a generous or stingy person (as explained in Avot 5:13, and based on related phrases in Devarim 15:9; 28:54,56). One who is stingy with his own possessions is likely to be jealous of the possessions of others. Only later, in the Amoraic period (for example Berachot 20a) did ayin hara come to be associated with an external, even magic, curse - "the evil eye."
Yetzer hara: This phrase, the "evil inclination", originates in Bereshit 6:5 and 8:21 - יֵצֶר לֵב הָאָדָם רַע, yetzer lev-ha-adam ra - "the inclination of man's heart was evil." In parallel, rabbinic texts also mention the yetzer hatov - "the good inclination", which motivates people to do good. This is certainly a more optimistic approach than the fatalistic conclusion that we are only inclined to evil. The mishna (Berachot 4:9) rules that we must serve God with both of our inclinations - the good and the evil.