etymology of “sesquicentennial”

The word sesquicentennial means "150th anniversary". When I first found this out, I thought about the prefix sesqui- and what it could mean.

My first thought was that it meant 6/4 = 1.5, because it seemed that the syllables matched up with "six" and "quart". After deciding that that must be right, I decided to check online. To my surprise, it appears that the prefix literally means "half and".

Was my first revelation a complete coincidence or is there actually a legitimate reason for what I noticed?

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6/4 would be a strange choice; the more common way of expressing that fraction is 3/2. – Dan Jun 10 '11 at 2:13
A strange choice, yes, but not entirely impossible. – Ben Alpert Jun 10 '11 at 2:32
Gamblers always refer to the relevant odds as 6/4 (pronounced six to four), not three to two. Old joke about the bookie teaching his baby to count : One, six-to-four, two... – TimLymington Jul 19 '11 at 11:09

Well, according to Lewis and Short's "A Latin Dictionary", the derivation is actually:

sesquĭ (sesque ),
I. num. adv. [perh. contr. from semis-qui], one half more, more by a half. As a separate word it occurs only once: “ut necesse sit partem pedis aut aequalem alteri parti aut altero tanto aut sesqui esse majorem,” Cic. Or. 56, 188. But freq. joined in one word with designations of number or quantity, with the signif. of once and a half. Joined with numerals (octavus and tertius), like the Gr. ἐπί (in ἐπόγδοος, ἐπίτριτος, etc.), it denotes an integer and such a fraction over as the numeral designates; v. sesquioctavus, etc.

so I'd be inclined to think "coincidence". From such things are folk etymologies made.

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Actually, sesqui- is a contraction of semis and que

According to etymonline:

"pertaining to a century and a half," 1880, from L. sesqui- "one and a half" (from semis "a half" + -que "and") + centennial (q.v.). First recorded ref. is to Baltimore's. sesquipedalian

Also dictionary.com

[from Latin, contraction of semi- + as as ² + -que and]

So, there aren't related, and I would say it is just coincidence.

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Yes, that's what I meant to say, sorry if that didn't come across. – Ben Alpert Jun 10 '11 at 3:38
Um, edited my answer to answer the question. :) – Thursagen Jun 10 '11 at 5:48