Pattern: Latin words that began with an ‘F’ tended to lose that initial ‘F’ sound and became silent (yet represented in writing with an ‘H’) as vulgar Latin turned into Spanish.
But upon closer look, it is a first cousin of both quash and squash.
All come from the Latin quassare, meaning, “to shatter.”
Thus, the qu-j for quejar maps to the qu-sh of quash and the sq-sh of squash.
Complaining, it seems, is a form of quashing (squashing?) your opponent!
The Spanish rehusar — literally, “refuse” — sounds odd to English ears: it’s the same word, but the -f- became an -h-. Huh?
This is explained via the pattern of Latin words that began with an f- tended to turn into an h- in Spanish and only in Spanish. See famine/hambre, and huir/fugitive for example.
Refuse and Rehusar follow the same pattern. Both come from the Latin refundere — from which we also get the English, refund. They are all ways of giving back.
This f-to-h pattern usually happens with the first letter of the word. But here it is the first letter of the second syllable — because the re- is of course the standard prefix so it didn’t effect the sound pattern change.
The Spanish celoso and the English for the same, jealousy, come from the same Greek root: zelos.
But how did this happen? They should so different!
The answer is that the Latin (and Greek) words with a -ch- sound and variations (like -sh-, the soft -j-, -z-, etc) usually turned into the hard, guttural, throat-cleaing -j- sound in Spanish. Think about sherry and jerez, for example, or quash and quejar, or soap and jabón.
Thus, the c-l-s of celoso maps to the j-l-s of jealous.
Curiously, the ancient Greek form — zelos — meant jealousy, but in the more positive sense of enthusiasm and friendly rivalry. In a word: zeal — which also comes from the same root!
Latin words that began with the fl- tended to become ll- in Spanish. This is consistent with the pattern in many other hard-constant-plus-L words, like pl- and cl-.
Who would’ve thunk?