I just knew there wouldn't be a consensus on this one. : )

here's the current state:
watchword \-werd\ noun (15c)
1 : a word or phrase used as a sign of recognition among members of the same society, class, or group
2 a : a word or motto that embodies a principle or guide to action of an individual or group : slogan <safety is our watchword>
b : a guiding principle <change is the watchword for both parties>

(C) 1996 Zane Publishing, Inc. and Merriam-Webster, Incorporated

thus, floccinaucinihilipilification is the wwftd watchword.

now, for the rest of the story...

watchword started out with a military sense of, wait for it... password (C 15); later it became the call of a sentinel on his rounds (C 17) or a signal to begin an attack (C 16). Shakespeare transferred this latter sense thus: Which gives the watch word to his hand ful soon, To draw the clowd that hides the silver Moon.
Subsequently it began to be used as in senses 1 and 2 above.
One other, now obsolete, use was as a cautionary word or warning event.

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