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I have a very similar story, finding this site around 12 years ago via Google and joining for the newsletters. (Thanks Kent for the daily zingers! )
Also like you, I spend the vast majority of my time here in the Lounge enjoying the wit, sarcasm, and mostly interesting conversations, thoughts, and rants of the cast here. There are some really smart and witty people here!
The answer is lummox. I can't believe that you guys didn't get this one. The word is right there in the list of synonyms. I just knew that as soon as someone bit shifted the hexadecimal the suffix would appear and give it away... there are only 4 or 5 words that end with 'MOX' in the English language with (lc > 3)
[PRIMARY CLUE PATH]
Gematriacally 0x00584f4d4d554c46 them: ('F'+('L'<<8)+('U'<<16)+('M'<<24)+('M'<<32)+('O'<<40)+('X'<<48) == "FLUMMOX"
crowning the luminous : LUM
oscillating : back and forth or left to right
by the fifth power of two : 32
oscillating 0x00584f4d4d554c46 by the fifth power of two : (0x00584f4d4d554c46 >>= 32) == 0x0000000000584f4d in ASCII == "MOX"
conjoined : lum mox
but will always be nincompoops : lummox
[ALTERNATE PREFIX CLUE PATH]
Gematriacally luminous : 0x53554f4e494d4c4c
oscillating 0x53554f4e494d4c4c by the fifth power of two : (0x53554f4e494d4c4c <<= 32) == 0x494d554c00000000 in ASCII == "LUMI"
crowning the luminous : "LUM"