Why is there an "h" in "pulchritude"?

I'd assumed that pulchritude was derived from Greek, because of the "ch" but it turns out to be from Latin pulcher. I've been taught that "c" always has a hard pronunciation in Latin, so why would there be an "h" there?

(Although pulchritude is an English word, this might be more relevant to a Latin StackExchange, which unfortunately doesn't exist yet.)

Solution 1:

In latin, ch was used to transcribe the Greek Χ (Chi) when it had a /kʰ/ sound (some regional forms of the alphabet used that letter where Ξ was used elsehwere, which is why our X looks like Χ).

This has left its mark on some English word, notably Christ and words derived from it (Christian, Christmas).

English pulchritude from Latin pulchritudo from Latin pulcher (beautiful) +‎ -tūdō (makes an abstract noun from an adjective like English -ity) is straightforward.

Where pulcher came from is unknown, and hence is why it had a ch. Maybe it was from a now lost Greek word. Maybe it had a /k/ sound or some other sound that got mutated and the spelling changed to match the /kʰ/ sound. Maybe it was borrowed from someone else entirely. Maybe some Roman bloke came up with some theory about why pulcher was more logical ;)

In any case, it did have the /kʰ/ sound, just as the English now has a /k/ sound of those ch words we got from Greek via Latin (again, Christ being another example).