These posts from this community have been super cool.

~~Fajitas are Fascist~~

Fascists are Fajitas

Fascinating

About Spanish: we know that the word wasn't directly inherited by Spanish because Latin /f/ typically becomes /h/ and then gets deleted (but it's still spelled as such); for example facere→hacer "to do" or filium→hijo "son". In fact the word faja does have a native albeit archaic cognate with ⟨h⟩, it's haza "thin strip of land".

Exceptions are typically

• when the /f/ was followed by /u/; see focum "hearth" → fuego "fire"
• posh words associated with the clergy and their ultraconservative speech; see fidem→fe "faith"
• side-borrowing;: as in the OP, fasciam "band" → Aragonese faixa "band, strip" → Spanish faja
• a random /h/ being kept and reinforced to /x/ for expletive powers; see futuere "to fuck vaginally" → *hoder → joder "to fuck"

The case of faggot* "bundle" is an interesting one. The word was borrowed from Old French fagot "bundle", in turn borrowed from Italian fagotto "bundle" (also a musical instrument, dunno the English name). However, past that, the etymology is disputed, and I don't buy the idea that fagotto comes from *facus←fascis, here's why.

Late Latin regularising -is into -us or -a is common, so a word like *fascus wouldn't be strange. But why was that /s/ dropped, if Italian is OK with medial /sk/? And it would need to be dropped early enough to allow a rather erratic /k/ ⟨c⟩ → /g/ shift, that doesn't even trigger regularly in Italian.

But let's say that the /s/ was dropped "because reasons". Why is the diminutive -ettus/-ittus, even if -culus/-ulus is more common? You'd probably end with *faculum→*facchio.

And, if you don't drop the /s/, you end with *fasculum→fascio. Cue to the word originating "fascism".

But, fine, let's use -ettus. You'd end with *facettum→*facetto, with a clear /tʃ/ sound. (French would've borrowed it as *fachet or similar).

Are you guys getting what I'm saying? You need a lot of improbable events to explain the word "faggot" as backtracking to "fascis".

My second best bet is barbarism. It might be worth to check for some similar word in Lombardic (the Germanic variety; not to be confused with Lombard), Italian did borrow a few of them.

*NOTE: I am using the word metalinguistically, to refer to itself, otherwise it's hard to talk about etymology. I am aware that it is often used to target marginalised individuals and groups based on their sexuality; however that is not what I am doing here.

fun fact, another term derived from fascis is- [BANNED]