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Is "lustrum" (pl. lustra) an understandable (say, at least in academic publications) or valid/common term for a five year span, e.g. to use in a table summarizing data where space can be very valuable? In other words:

  • Is "lustrum" archaic?
  • Is "pentad" an alternative?
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'five years' is what one normally uses in English. – Mitch Jul 29 '12 at 22:53
How about quincade? – Pitarou Jul 30 '12 at 13:14
up vote 8 down vote accepted

This website says the last lustrum was held in a.d. 74 by Vespasian. So I would say, no, lustrum is not the word you're looking for. Pentad is not in some dictionaries, and the one I found that does have it defines it as "a group of five". So that's not the word you're looking for, either. I would suggest

5 yr span

if you're trying to squeeze it into as short a space as possible. Quinquennium does mean what you want it to, but it's quite rare and fairly long.

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You might as well say that because gladiatorial games were abolished in the 4th century, nobody will understand gladiator. I don't think there's anything wrong with lustrum. – TimLymington Jun 7 '11 at 22:33
@Tim: Well, if Lustrum was also the name of a recent Academy Award-winning film, it sure would help. – Callithumpian Jun 8 '11 at 0:21
I'm going to work "quinquennium" into a conversation soon. – Malvolio Jun 8 '11 at 1:53
Diving into ngrams, lustrum is apparently not as rare as I’d thought: here, compare it with another somewhat arbitrary selection of words. However, I share with other answerers the feeling that few English speakers would understand it (especially without a clarifying context). – PLL Jun 8 '11 at 5:38
Pentad has the advantage that people are more likely to be able to guess at least the five part of the meaning (by analogy with pentagon, pentagram and other words of similar Greek origin). Lustrum would leave me guessing. – psmears Jun 8 '11 at 11:39

The need for this word came up for me recently at work. Pentad may not be technically right but I do like it. As Psmears points out, many people will know "penta" means five. Also "tad" means small. A Pentad is smaller than a decade.

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