In my opinion this is the only meaning that justifies its use: "to the extent that".
For all other purposes there is "in that", "as far as", sometimes simply "if" and "when".
Some examples:
The depiction of sex in the show is arguably one of its distinctive aspects, and cheesy only insofar as sex is fundamentally absurd.
(The Atlantic)
I am obliged, in so far as I am able, to write about the world as I find it to be.
(The Age)
I completely understand your problem. I have been there!
The problem with non-native speakers is that they want to use more words in their speeches and writing to sound better without knowing how and where to place those words and when!
As non-native speakers, we often ignore the 'type' of the word, its pronunciation (a big factor for us!) and the word's placement.
The Solution:
Don't just check the type and meaning of the word; focus more on **how the word is used* through examples on standard dictionaries like OALD, MW, Collin's, and Longman's etc.
Take my own example. Years back, I had the same problem. I had come across the word 'admire'. I read the meaning but ignored something that was also written there in the dictionary (because it was not the part of word's 'meaning').
I then started using the word 'admire'.
Do you know that Mike raised his voice against the corruption in the college ~ Yes, I admire!
I was happy using the word. But was it right? NO!
What I had ignored was the type of verb it was! Transitive verb! This means, this word requires an object after it. Means, 'admire what?' is required.
So, then on, I was very conscious using the word.
Do you know that Mike raised his voice against the corruption in the college ~ Yes, I admire his courage!
So, my suggestion is that maintain a document, write down those new words, and most importantly along with their meaning, also write down the examples like how they are used.
At times, looking at an example or two won't serve the purpose. Check on other dictionaries and more examples from them. Once you are confirmed about the usage, simply memorize it!
Best Answer
Hapless means "without hap", and "hap" came to English from the same folk who brought the Danegeld to England and lutefisk to Minnesota: the Scandinavians. It's a very old word, and means "good fortune", and at its root, chance or eventuality. It's at the root of countless other words like happy, mishap, and happen, (which may be a vestige of the inflected verb hap). "Hapless" in English conjures a vision of Joe Btfsplk:
It's much unluckier than just unlucky. It's downright dismal.
The adjective Dismal was originally a noun, and comes to English from the Latin dies mali ("evil days") by way of the Old French dis mal. Until the 1400's, there were still noted on many calendars some days which were deemed unlucky. The OED tells us:
By extension the noun "dismal" was used to describe anyone or anything that smacked of evil, the Devil, death, gloom, or ill fortune. By 1621, it was a familiar adjective, and Robert Burton writes in the abstract to his Anatomy of Melancholy:
It was still used attributively and as a noun in the 18th century; President John Adams of the United States wrote to his wife in 1774:
Dismal is still in use today, both as an adjective that means "boding or bringing misfortune and disaster; unlucky, sinister, malign, fatal" † and as "A local name of dreary tracts of swampy land on the eastern sea-board of the United States, esp. in North Carolina." ‡:
A Dismal in North Carolina
In commentary to your question, you mention that in studying for your ITELS and TOEFL tests, you learned a "bunch of words that looked close to each other in meaning and weird to use." It's certainly true that hapless and dismal could sound weird in the wrong context; yet consider that a "weird" word may be just the right choice. Hapless is very widely used today to describe the unfortunate:
(The New Yorker, Jul 4, 2017)
The best advice to a student of English is to cherish the depth and richness of our polyglot tongue, to savor its oddities, to read everything you can get your hands on, and to listen to conversation to understand when a choice of words is dismal, or a speaker hapless. Someday, you may well overhear teenagers leaving a concert and saying:
† ‡Oxford English Dictionary
* The Week, June 25, 2017