If it's a short vowel sound and a single consonant, then you double the consonant to signify that the vowel sound is supposed to stay short:
map > mappable
hit > hittable
cancel > cancellable
Otherwise (if the vowel is already long, or if there is more than one consonant already) you don't need to double anything, because the vowel sound won't change anyway:
junk > junkable
excite > excitable
quote > quotable
If you don't double the consonant when you're supposed to, it will look like the vowel is supposed to be long:
mapable = "may-puh-bull", not "map-uh-bull"
Meaning
These two verbs lend and borrow often cause confusion for learners. The main reason is that many languages use just one verb for both of these meanings
The verb lend is like the verb give. It means to give temporarily, not permanently.
The verb borrow is more like the verb take. If you borrow something you are taking it, but temporarily, not permanently.
Grammar
The verb lend has the same grammar as the verb give. It takes an Indirect Object (the person your giving the thing to) and a Direct Object (the thing that you are giving):
- He gave me a pen.
- He lent me a pen.
The verb borrow has the same grammar as the verb take. It normally takes a Direct Object (the thing being taken) and it sometimes also takes a preposition phrase headed by the preposition from:
- I took a pen from him.
- I borrowed a pen from him.
The Original Poster's question
*When I was in trouble he borrowed me money. (ungrammatical)
When I was in trouble he lent me money.
Sentence (1) is incorrect for two reasons. Firstly the subject of the sentence he is giving the money, not taking it. Therefore we need the verb lend not the verb borrow.
Secondly the grammar in sentence (1) is problematic. The verb borrow cannot take an Indirect Object. We can't say "borrow me" in standard English.
Sentence (2) is, of course, perfectly fine. The poster could make a similar sentence with the word borrow, but this would need a different Subject:
When I was in trouble I borrowed money from him.
However, this sentence has a completely different feeling to it.
[Note:
This is the first installment of a post. The second installment will be much more complicated and will show how He borrowed me some money could be correct but not if me is a normal Object.
It might be worth noting that in some regional varieties of English we can use the verb borrow with the same grammar and meaning as lend, but this does not happen in standard Englishes like Southern Standard British English or General American.]
Best Answer
"Extend" is strictly a verb.
"Extent" is strictly a noun.